diff --git a/README.md b/README.md
index 6474f470a1..40c29b6b81 100644
--- a/README.md
+++ b/README.md
@@ -30,6 +30,7 @@ BIDS currently supports the following data modalities with more to come in the f
 - microscopy
 - NIRS
 - motion
+- MRS
 
 # Formatting your data with BIDS
 
diff --git a/mkdocs.yml b/mkdocs.yml
index 114e05c135..cfbdba2a49 100644
--- a/mkdocs.yml
+++ b/mkdocs.yml
@@ -19,6 +19,7 @@ nav:
           - Microscopy: modality-specific-files/microscopy.md
           - Near-Infrared Spectroscopy: modality-specific-files/near-infrared-spectroscopy.md
           - Motion: modality-specific-files/motion.md
+          - Magnetic Resonance Spectroscopy: modality-specific-files/magnetic-resonance-spectroscopy.md
       - Derivatives:
           - BIDS Derivatives: derivatives/introduction.md
           - Common data types and metadata: derivatives/common-data-types.md
diff --git a/src/appendices/cross-modality-correspondence.md b/src/appendices/cross-modality-correspondence.md
index c71a1c73f5..6dba22b325 100644
--- a/src/appendices/cross-modality-correspondence.md
+++ b/src/appendices/cross-modality-correspondence.md
@@ -12,3 +12,10 @@ The reason for this is that the MRI needs to be corrected for nonlinear gradient
 in order to fit the accompanying PET scans for co-registration
 (Knudsen et al. 2020, [doi:10.1177/0271678X20905433](https://doi.org/10.1177/0271678X20905433);
 Norgaard et al. 2019, [doi:10.1016/j.neuroimage.2019.05.055](https://doi.org/10.1016/j.neuroimage.2019.05.055)).
+
+## MRS-MRI correspondence
+
+It is typical to acquire high-resolution 3D anatomical MR images alongside MRS data for
+voxel/slab placement, co-registration, and partial-volume tissue correction of metabolite concentrations.
+To avoid incorrectly matching an MRS dataset with a corresponding anatomical MR image,
+it is RECOMMENDED that the field `AnatomicalImage` be included in the MRS sidecar JSON files.
diff --git a/src/introduction.md b/src/introduction.md
index 4315720e3a..a07b654b2c 100644
--- a/src/introduction.md
+++ b/src/introduction.md
@@ -184,6 +184,10 @@ For example:
      PsyArXiv.
      [doi:10.31234/osf.io/w6z79](https://doi.org/10.31234/osf.io/w6z79)
 
+#### MRS
+
+-   (publication forthcoming)
+
 ### Research Resource Identifier (RRID)
 
 BIDS has also a
diff --git a/src/modality-specific-files/magnetic-resonance-spectroscopy.md b/src/modality-specific-files/magnetic-resonance-spectroscopy.md
new file mode 100644
index 0000000000..22ec6540e0
--- /dev/null
+++ b/src/modality-specific-files/magnetic-resonance-spectroscopy.md
@@ -0,0 +1,260 @@
+# Magnetic Resonance Spectroscopy
+
+Support for Magnetic Resonance Spectroscopy (MRS) was developed as a
+[BIDS Extension Proposal](../extensions.md#bids-extension-proposals).
+Please see [Citing BIDS](../introduction.md#citing-bids)
+on how to appropriately credit this extension when referring to it in the
+context of the academic literature.
+
+!!! example "Example datasets"
+
+    Several [example MRS datasets](https://github.com/bids-standard/bids-examples/pull/425) have
+    been formatted using this specification and can be used for practical guidance when curating a new
+    dataset.
+
+## MRS data
+
+<!--
+This block generates filename templates.
+The inputs for this macro can be found in the directory
+  src/schema/rules/files/raw
+and a guide for using macros can be found at
+ https://github.com/bids-standard/bids-specification/blob/master/macros_doc.md
+-->
+{{ MACROS___make_filename_template("raw", datatypes=["mrs"]) }}
+
+MRS is a spectroscopic technique based on the phenomenon of nuclear magnetic resonance
+that allows for the noninvasive detection and quantification of molecules in biochemical samples, such as brain tissue.
+It can be conducted in humans using conventional MRI systems.
+
+Due to the diversity in manufacturers' MRS data file formats, source data MUST be converted into the
+[NIfTI-MRS format](https://wtclarke.github.io/mrs_nifti_standard/) (`*.nii[.gz]`) ([doi:10.1002/mrm.29418](https://doi.org/10.1002/mrm.29418)).
+This format is based on the NIfTI framework and is designed to accommodate the nuances of raw MRS data.
+All necessary information to parse this `*.nii[.gz]` file (for example, spectrometer frequency, echo time,
+repetition time, and so on) are stored in a JSON header extension.
+Conversion of proprietary MRS file formats to NIfTI-MRS and extraction of some (but not all) BIDS-compliant metadata can be performed
+using [spec2nii](https://github.com/wtclarke/spec2nii).
+Note that the "rawness" of data stored in the NIfTI-MRS file will depend on the format of the source data.
+It is RECOMMENDED that users export their source data from the scanner in an appropriately raw format prior to conversion.
+
+For MRSI data, "raw" signifies spatially reconstructed data (that is, data in image space rather than (*k*,*t*)-space),
+given the complexity and diversity of sampling approaches.
+Note that NIfTI-MRS is not designed to store data that has not been spatially reconstructed.
+
+Regarding source data, each manufacturer has its own file format (sometimes multiple formats) for exporting MRS data from
+the MRI scanner console for offline processing.
+GE exports a P-file (`*.7`) that stores unprocessed, un-coil-combined data with metadata embedded
+in a proprietary data header.
+Philips has multiple export formats, the most common being the SDAT/SPAR format.
+The `*.sdat` file contains either each coil-combined transient stored separately
+or all transients summed into a signal average.
+The `*.spar` file is a plaintext file describing acquisition parameters.
+It is also possible to export raw data as `*.data`/`*.list` or DICOM files.
+Siemens scanners allow data export in four formats: i) a proprietary DICOM-structured file known as IMA (`*.ima`);
+ii) a conventional DICOM MR Spectroscopy Storage format (`*.dcm`); iii) RDA (`*.rda`),
+a proprietary file format with a text-formatted header followed by the binary data points;
+and iv) TWIX (`*.dat`), a proprietary file format designed for storing unreconstructed, unprocessed MRS data
+from each individual coil element.
+The IMA, DICOM MRS, and RDA formats are typically used to export reconstructed and processed data;
+however, the sequence designer may choose to also allow the export of un-averaged transients
+or data from individual coil elements.
+Bruker data are are exported as two binary files: one file stores each transient separately,
+while the other stores the sum of the transients.
+A separate plaintext file stores the sequence name, voxel position, voxel orientation, and other metadata.
+All of these files are considered source data and, if present, MUST be stored in the
+[`sourcedata`](../common-principles.md#source-vs-raw-vs-derived-data) directory.
+
+### Single-voxel spectroscopy and MRS imaging
+
+| **Name**                                 | **`suffix`** | **Description**                                                                                                                                                                        |
+| ---------------------------------------- | ------------ | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
+| Single-voxel spectroscopy                | svs          | MRS acquisitions where the detected MR signal is spatially localized to a single volume.                                                                                               |
+| Magnetic resonance spectroscopic imaging | mrsi         | MRS acquisitions where additional imaging gradients are used to detect the MR signal from 1, 2, or 3 spatial dimensions.                                                               |
+| Unlocalized spectroscopy                 | unloc        | MRS acquisitions run without localization. This includes signals detected using coil sensitivity only.                                                                                 |
+| Concentration or calibration reference   | mrsref       | An MRS acquisition collected to serve as a concentration reference for absolute quantification or as a calibration reference for preprocessing (for example, eddy-current correction). |
+
+A major distinction between MRS acquisitions is whether the acquisition technique probes spectral
+information from a single volume (single-voxel spectroscopy, SVS) or encodes this information along
+1, 2, or 3 spatial dimensions resulting in multiple sub-volumes (MRS imaging, MRSI).
+To avoid confusion, the suffixes `svs` and `mrsi` MUST be used to distinguish the two techniques.
+For cases where localization is not used, the suffix `unloc` MUST be used.
+
+Furthermore, it is common to acquire an additional MRS dataset that may serve as a reference for
+scaling metabolite signal levels (for example, to obtain concentrations) and/or for preprocessing steps (such as
+eddy-current correction, RF coil combination, phasing, and frequency calibration).
+This could be either an external reference (for example, a phantom or a synthetic signal) or, more typically,
+an internal tissue water reference.
+For such datasets, the suffix `mrsref` MUST be used.
+Should multiple references exist for a given dataset, the user MAY use the `acq-<label>` entity to distinguish the files.
+For example, `sub-01_acq-conc_mrsref.nii.gz` and `sub-01_acq-ecc_mrsref.nii.gz` could be used to name
+two references to be used for concentration scaling and eddy-current correction, respectively.
+
+### MRS sequences
+
+Given the large variety of MRS sequences, there will be times when providing sufficient detail of
+acquisition parameters in filenames is helpful or necessary to distinguish datasets in a given study.
+
+Here we present a set of labels that can be used when using the `acq-<label>` entity in the filename.
+These are based on the most commonly used in vivo MRS sequences/techniques, and are OPTIONAL to use.
+Users are free to choose any label they wish as long as they are consistent across participants
+and sessions and use only legal label characters.
+If used, the chosen label SHOULD also be described in the `PulseSequenceType` field in the sidecar JSON file.
+
+| **Name**                                    | **`label`** | **Description**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
+| ------------------------------------------- | ----------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
+| PRESS                                       | press       | A double spin-echo sequence that achieves spatial localization by employing three slice-selective RF pulses: 90°–180°–180°–acq.                                                                                                                                                                                                                                                                                                                                                                                   |
+| STEAM                                       | steam       | A stimulated-echo sequence that uses three 90° slice-selective pulses for spatial localization.                                                                                                                                                                                                                                                                                                                                                                                                                   |
+| LASER                                       | laser       | LASER uses three pairs of slice-selective 180° adiabatic full-passage (AFP) refocusing pulses for localization. These are preceded by a non-slice-selective adiabatic half-passage (AHP) excitation pulse.                                                                                                                                                                                                                                                                                                        |
+| sLASER                                      | slaser      | sLASER is a modification of LASER where the AHP and first pair of AFP pulses are replaced with a non-adiabatic slice-selective 90° excitation pulse, typically employed to reduce the minimum TE.                                                                                                                                                                                                                                                                                                                 |
+| SPECIAL                                     | special     | SPECIAL is a two-shot experiment. In the first shot, a pre-excitation slice-selective 180° AFP inversion pulse precedes a spin-echo acquisition with slice selection (90°–180°–acq). In the second shot, the adiabatic pulse is not applied. The 3D localized signal is derived by subtracting the two shots.                                                                                                                                                                                                     |
+| MEGA                                        | mega        | MEGA is a spectral editing technique that applies narrowband frequency-selective 180° pulses to refocus *J*-coupled spins at a specific frequency without affecting the spins of metabolites with resonances beyond the frequency range. Applying these pulses in alternating scans (for example, edit ON and edit OFF) and then subtracting the ON/OFF pairs results in a *J*-difference-edited spectrum that removes the unedited signals, leaving only those signals that were affected by the editing pulses. |
+| HERMES                                      | hermes      | HERMES is an extension of MEGA editing whereby the two-step experiment becomes a four-step experiment. This permits multiple metabolites to be edited in a multiplexed manner. By employing Hadamard combination of the four edited sub-spectra, HERMES can reveal several metabolites unambiguously.                                                                                                                                                                                                             |
+| HERCULES                                    | hercules    | HERCULES is a different flavor of HERMES that targets more metabolites using the same four-step experiment.                                                                                                                                                                                                                                                                                                                                                                                                       |
+| Multiple quantum coherence (MQC) editing    | mqc         | MQC editing targets *J*-coupled resonances by selecting desired coherence pathways using MQ gradients and frequency-selective RF pulses.                                                                                                                                                                                                                                                                                                                                                                          |
+| Localized correlation spectroscopy (L-COSY) | lcosy       | L-COSY is a 2D MRS technique whereby one of the interpulse durations is changed sequentially. A 2D Fourier transform produces a 2D spectrum that displays singlets on the diagonal and *J*-coupled metabolites on the off-diagonal, with the offsets equal to the *J*-coupling constants.                                                                                                                                                                                                                         |
+| *J*-resolved spectroscopy                   | j           | Another 2D technique, where in a *J*-resolved acquisition, a series of transients are collected at different TEs. A 2D Fourier transform is applied to generate a 2D spectrum where one dimension characterizes both chemical shift and *J*-coupling and the other only *J*-coupling.                                                                                                                                                                                                                             |
+| Diffusion-weighted (DW) spectroscopy        | dw          | The diffusion of intracellular metabolites can be characterized using DW spectroscopy. In such acquisitions, the strength of gradients in a conventional MRS sequence is modulated to sensitize the metabolite signals to diffusion.                                                                                                                                                                                                                                                                              |
+| FID spectroscopy                            | fid         | FID spectroscopy is a pulse-acquire acquisition where an excitation pulse is followed by direct acquisition of the FID. This approach is most often used in MRSI (that is, FID-MRSI) when combined with slice- or slab-selection.                                                                                                                                                                                                                                                                                 |
+| Metabolite-cycled (MC) spectroscopy         | mc          | MC spectroscopy involves the use of asymmetric adiabatic inversion of the upfield and downfield parts of the MR spectrum, allowing for simultaneous acquisition of water and metabolite spectra.                                                                                                                                                                                                                                                                                                                  |
+| Spin-echo spectroscopy                      | spinecho    | An MRS experiment whereby the MR signal is detected using a spin-echo acquisition: 90°–180°–acq.                                                                                                                                                                                                                                                                                                                                                                                                                  |
+
+Each `<label>` in the table above MAY be combined with another to better describe the acquisition used.
+For example, `megaspecial`, `jpress`, `dwslaser`, `mcdwsteam`, and so on.
+
+The OPTIONAL `nuc-<label>` entity can be used to distinguish acquisitions tuned to detect different nuclei.
+The label is the name of the nucleus or nuclei, which corresponds to DICOM Tag 0018, 9100.
+For example, `nuc-1H`, `nuc-31P`, `nuc-1H13C`.
+If used, the field `ResonantNucleus` MUST also be included in the corresponding sidecar JSON file, using the same label.
+
+Similarly, the OPTIONAL `voi-<label>` entity can be used to distinguish between
+acquisitions localized to different regions (that is, acquisitions with different VOI).
+The label SHOULD be the name of the body region or part scanned.
+If used, the fields `BodyPart` and `BodyPartDetails` MUST also be included in the corresponding sidecar JSON file.
+`BodyPartDetailsOntology` is OPTIONAL to also include.
+
+## Sidecar JSON
+
+MRS data files MUST be described by metadata fields, stored in sidecar JSON files (`*.json`).
+
+### Common metadata fields
+
+Metadata described in the following sections are shared with other MR modalities that SHOULD
+or MAY be present in the sidecar JSON files.
+
+#### Scanner hardware
+
+<!-- This block generates a metadata table.
+These tables are defined in
+  src/schema/rules/sidecars
+The definitions of the fields specified in these tables may be found in
+  src/schema/objects/metadata.yaml
+A guide for using macros can be found at
+ https://github.com/bids-standard/bids-specification/blob/master/macros_doc.md
+-->
+{{ MACROS___make_sidecar_table("mrs.MRSScannerHardware") }}
+
+#### Sequence specifics
+
+<!-- This block generates a metadata table.
+These tables are defined in
+  src/schema/rules/sidecars
+The definitions of the fields specified in these tables may be found in
+  src/schema/objects/metadata.yaml
+A guide for using macros can be found at
+ https://github.com/bids-standard/bids-specification/blob/master/macros_doc.md
+-->
+{{ MACROS___make_sidecar_table("mrs.MRSSequenceSpecifics") }}
+
+#### Tissue description
+
+<!-- This block generates a metadata table.
+These tables are defined in
+  src/schema/rules/sidecars
+The definitions of the fields specified in these tables may be found in
+  src/schema/objects/metadata.yaml
+A guide for using macros can be found at
+ https://github.com/bids-standard/bids-specification/blob/master/macros_doc.md
+-->
+{{ MACROS___make_sidecar_table("mrs.MRSSample") }}
+
+### MRS-relevant fields
+
+Metadata fields that MUST be present:
+
+<!-- This block generates a metadata table.
+These tables are defined in
+  src/schema/rules/sidecars
+The definitions of the fields specified in these tables may be found in
+  src/schema/objects/metadata.yaml
+A guide for using macros can be found at
+ https://github.com/bids-standard/bids-specification/blob/master/macros_doc.md
+-->
+{{ MACROS___make_sidecar_table([
+  "mrs.MRSRequiredFields",
+  ])
+}}
+
+Metadata fields that SHOULD be present:
+
+<!-- This block generates a metadata table.
+These tables are defined in
+  src/schema/rules/sidecars
+The definitions of the fields specified in these tables may be found in
+  src/schema/objects/metadata.yaml
+A guide for using macros can be found at
+ https://github.com/bids-standard/bids-specification/blob/master/macros_doc.md
+-->
+{{ MACROS___make_sidecar_table([
+  "mrs.MRSRecommendedFields",
+  "mrs.MRSRepetitionTime",
+  "mrs.MRSVolumeTiming",
+  "mrs.MRSConditionalNumTransients",
+  "mrs.MRSIRecommendedFields",
+  "mrs.MRSConditionalInversionTime",
+  "mrs.MRSConditionalAnatomicalImage",
+  ])
+}}
+
+Metadata fields that MAY be present:
+
+<!-- This block generates a metadata table.
+These tables are defined in
+  src/schema/rules/sidecars
+The definitions of the fields specified in these tables may be found in
+  src/schema/objects/metadata.yaml
+A guide for using macros can be found at
+ https://github.com/bids-standard/bids-specification/blob/master/macros_doc.md
+-->
+{{ MACROS___make_sidecar_table([
+  "mrs.MRSOptionalFields",
+  ])
+}}
+
+### Example `*_svs.json`
+
+```JSON
+{
+  "InstitutionName": "Weill Cornell Medicine",
+  "InstitutionAddress": "1300 York Avenue, New York, NY 10065, USA",
+  "Manufacturer": "GE",
+  "ManufacturersModelName": "Discovery MR750",
+  "MagneticFieldStrength": 3,
+  "PulseSequenceType": "PRESS",
+  "ResonantNucleus": "1H",
+  "SpectrometerFrequency": 127.771,
+  "SpectralWidth": 2000,
+  "EchoTime": 0.035,
+  "NumberOfSpectralPoints": 2048,
+  "NumberOfTransients": 64,
+  "RepetitionTime": 2,
+  "AcquisitionVoxelSize": [40, 20, 30],
+  "BodyPart": "BRAIN",
+  "BodyPartDetails": "Anterior cingulate cortex",
+  "ReferenceSignal": "bids::sub-01/mrs/sub-01_acq-press_mrsref.nii.gz",
+  "AnatomicalImage": "bids::sub-01/anat/sub-01_T1w.nii.gz"
+}
+```
+
+## Combining MRS with anatomical MRI
+
+For combining MRS data with anatomical MRI data, see [MRS-MRI correspondence](../appendices/cross-modality-correspondence.md#mrs-mri-correspondence) in the Appendix.
diff --git a/src/schema/meta/context.yaml b/src/schema/meta/context.yaml
index f80a23d363..2481e15d99 100644
--- a/src/schema/meta/context.yaml
+++ b/src/schema/meta/context.yaml
@@ -405,6 +405,10 @@ properties:
         name: 'sform code'
         description: 'Use of the affine fields.'
         type: integer
+      mrs:
+        name: 'NIfTI-MRS extension'
+        description: 'NIfTI-MRS JSON fields'
+        type: object
   ome:
     name: 'Open Microscopy Environment fields'
     description: 'Parsed contents of OME-XML header, which may be found in OME-TIFF or OME-ZARR files'
diff --git a/src/schema/objects/common_principles.yaml b/src/schema/objects/common_principles.yaml
index 7e669efb52..06a1fa53d0 100644
--- a/src/schema/objects/common_principles.yaml
+++ b/src/schema/objects/common_principles.yaml
@@ -41,6 +41,9 @@ data_type:
         12. `nirs` (near infrared spectroscopy)
 
         13. `motion` (motion)
+
+        14. `mrs` (magnetic resonance spectroscopy)
+
 dataset:
   display_name: Dataset
   description: |
diff --git a/src/schema/objects/datatypes.yaml b/src/schema/objects/datatypes.yaml
index c51fa41382..e84f1a6ba6 100644
--- a/src/schema/objects/datatypes.yaml
+++ b/src/schema/objects/datatypes.yaml
@@ -47,6 +47,10 @@ motion:
   value: motion
   display_name: Motion
   description: Motion data from a tracking system
+mrs:
+  value: mrs
+  display_name: Magnetic Resonance Spectroscopy
+  description: Magnetic resonance spectroscopy data
 perf:
   value: perf
   display_name: Perfusion imaging
diff --git a/src/schema/objects/entities.yaml b/src/schema/objects/entities.yaml
index 6facc34c0d..ee5ab67534 100644
--- a/src/schema/objects/entities.yaml
+++ b/src/schema/objects/entities.yaml
@@ -179,6 +179,17 @@ mtransfer:
   enum:
     - $ref: objects.enums.on__mtransfer.value
     - $ref: objects.enums.off__mtransfer.value
+nucleus:
+  name: nuc
+  display_name: Nucleus
+  description: |
+    The `nuc-<label>` entity can be used to distinguish acquisitions tuned
+    to detect different nuclei.
+    The label is the name of the nucleus or nuclei, which corresponds to DICOM Tag `0018, 9100`.
+    If present in the filename, `"ResonantNucleus"` MUST also be included in
+    the associated metadata.
+  type: string
+  format: label
 part:
   name: part
   display_name: Part
@@ -408,9 +419,19 @@ tracer:
     Please note that the `<label>` does not need to match the actual value of the field.
   type: string
   format: label
+volume:
+  name: voi
+  display_name: Volume of Interest
+  description: |
+    The `voi-<label>` entity can be used to distinguish acquisitions localized to different regions.
+    The label SHOULD be the name of the body region or part scanned.
+    If used, the fields `"BodyPart"` and `"BodyPartDetails"` MUST be defined in the JSON file.
+    `BodyPartDetailsOntology` is OPTIONAL to also include.
+  type: string
+  format: label
 tracksys:
   name: tracksys
-  display_name: Tracking system
+  display_name: Tracking System
   description: |
     The `tracksys-<label>` entity can be used as a key-value pair
     to label *_motion.tsv and *_motion.json files.
diff --git a/src/schema/objects/enums.yaml b/src/schema/objects/enums.yaml
index 2f63006460..6c43592c9f 100644
--- a/src/schema/objects/enums.yaml
+++ b/src/schema/objects/enums.yaml
@@ -120,6 +120,11 @@ Absent:
   display_name: Absent
   description: |
     No specific M0 information is present.
+OneD:
+  value: 1D
+  display_name: One-dimensional
+  description: |
+    One-dimensional MR acquisition.
 TwoD:
   value: 2D
   display_name: Two-dimensional
diff --git a/src/schema/objects/metadata.yaml b/src/schema/objects/metadata.yaml
index d9222005a1..d99fcc599b 100644
--- a/src/schema/objects/metadata.yaml
+++ b/src/schema/objects/metadata.yaml
@@ -37,7 +37,7 @@ AcquisitionVoxelSize:
   display_name: Acquisition Voxel Size
   description: |
     An array of numbers with a length of 3, in millimeters.
-    This parameter denotes the original acquisition voxel size,
+    This field denotes the original acquisition voxel size,
     excluding any inter-slice gaps and before any interpolation or resampling
     within reconstruction or image processing.
     Any point spread function effects, for example due to T2-blurring,
@@ -70,6 +70,20 @@ AnalyticalApproach:
     - type: array
       items:
         type: string
+AnatomicalImage:
+  name: AnatomicalImage
+  display_name: Anatomical Image
+  description: |
+    The path(s) to the anatomical MR image file(s), if present,
+    to which the associated MRS data file corresponds.
+    Contains one or more [BIDS URIs](SPEC_ROOT/common-principles.md#bids-uri).
+  anyOf:
+    - type: string
+      format: bids_uri
+    - type: array
+      items:
+        type: string
+        format: bids_uri
 AnatomicalLandmarkCoordinateSystem:
   name: AnatomicalLandmarkCoordinateSystem
   display_name: Anatomical Landmark Coordinate System
@@ -236,14 +250,14 @@ B0ShimmingTechnique:
   name: B0ShimmingTechnique
   display_name: B0 Shimming Technique
   description: |
-    The technique used to shim the *B<sub>0</sub>* field (for example, `"Dynamic shim updating"`
+    The technique used to shim the *B*<sub>0</sub> field (for example, `"Dynamic shim updating"`
     or `"FASTMAP"`).
   type: string
 B1ShimmingTechnique:
   name: B1ShimmingTechnique
   display_name: B1 Shimming Technique
   description: |
-    The technique used to shim the *B<sub>1</sub>* field (for example, `"Simple phase align"`
+    The technique used to shim the *B*<sub>1</sub> field (for example, `"Simple phase align"`
     or `"Pre-saturated TurboFLASH"`).
   type: string
 BIDSVersion:
@@ -402,6 +416,22 @@ CellType:
     Values SHOULD come from the
     [cell ontology](https://obofoundry.org/ontology/cl.html).
   type: string
+ChemicalShiftOffset:
+  name: ChemicalShiftOffset
+  display_name: Chemical Shift Offset
+  description: |
+    The chemical shift at the center of `SpectralWidth` corresponding to 0 Hz,
+    specified in ppm (for example, `4.65`).
+  type: number
+  unit: ppm
+ChemicalShiftReference:
+  name: ChemicalShiftReference
+  display_name: Chemical Shift Reference
+  description: |
+    The chemical shift at the transmitter frequency, specified in ppm (for example, `2.68`).
+    Corresponds to DICOM Tag 0018, 9053 `Chemical Shift Reference`.
+  type: number
+  unit: ppm
 ChunkTransformationMatrix:
   name: ChunkTransformationMatrix
   display_name: Chunk Transformation Matrix
@@ -844,6 +874,13 @@ EOGChannelCount:
     Number of EOG channels.
   type: integer
   minimum: 0
+EchoAcquisition:
+  name: EchoAcquisition
+  display_name: Echo Acquisition
+  description: |
+    How the detected echo was acquired when the analog-to-digital converter was turned on.
+    For example, `"Half echo"`, `"Full echo"`.
+  type: string
 EchoTime:
   name: EchoTime
   display_name: Echo Time
@@ -856,12 +893,6 @@ EchoTime:
     [file collection](SPEC_ROOT/appendices/file-collections.md)
     where the value of this field is iterated using the
     [`echo` entity](SPEC_ROOT/appendices/entities.md#echo).
-    The data type array provides a value for each volume in a 4D dataset and
-    should only be used when the volume timing is critical for interpretation
-    of the data, such as in
-    [ASL](SPEC_ROOT/modality-specific-files/magnetic-resonance-imaging-data.md#\
-    arterial-spin-labeling-perfusion-data)
-    or variable echo time fMRI sequences.
   anyOf:
     - type: number
       unit: s
@@ -896,6 +927,55 @@ EchoTime__fmap:
   type: number
   unit: s
   exclusiveMinimum: 0
+EditCondition:
+  name: EditCondition
+  display_name: Editing Condition
+  description: |
+    If spectral editing was applied, this lists the application order of `"EditPulse"`.
+    For example, `["ON", "OFF"]` for a MEGA-edited experiment or
+    `["A", "B", "C", "D"]` for a HERMES-edited experiment.
+  anyOf:
+    - type: string
+    - type: array
+      items:
+        type: string
+EditPulse:
+  name: EditPulse
+  display_name: Editing Pulse
+  description: |
+    If spectral editing was applied, this details the editing parameters.
+    For example:
+    `{"ON": {"FrequencyOffset": 1.9, "PulseDuration": 16},
+    "OFF": {"FrequencyOffset": 7.5, "PulseDuration": 16}}`.
+  type: object
+  additionalProperties:
+    type: object
+    recommended_fields: [FrequencyOffset, PulseDuration]
+    properties:
+      FrequencyOffset:
+        anyOf:
+          - type: number
+            unit: ppm
+          - type: array
+            items:
+              type: number
+              unit: ppm
+      PulseDuration:
+        type: number
+        unit: ms
+EditTarget:
+  name: EditTarget
+  display_name: Editing Target
+  description: |
+    If spectral editing was applied, this describes the metabolites that were selectively targeted
+    (for example, `"GABA"` or `"Lac"`).
+    If multiple metabolites were targeted (for example, in a HERMES acquisition),
+    an array can be used: `["GABA", "GSH"]`.
+  anyOf:
+    - type: string
+    - type: array
+      items:
+        type: string
 EffectiveEchoSpacing:
   name: EffectiveEchoSpacing
   display_name: Effective Echo Spacing
@@ -945,6 +1025,14 @@ ElectrodeManufacturersModelName:
     If different electrode types are used,
     please use the corresponding table in the `_electrodes.tsv` file.
   type: string
+EncodingTechnique:
+  name: EncodingTechnique
+  display_name: Encoding Technique
+  description: |
+    The encoding technique used during readout.
+    For example, `"Cartesian"`, `"EPSI"`, `"Spiral"`,
+    or `"Density-weighted concentric ring trajectory"`.
+  type: string
 EpochLength:
   name: EpochLength
   display_name: Epoch Length
@@ -1050,12 +1138,6 @@ FlipAngle:
     [file collection](SPEC_ROOT/appendices/file-collections.md)
     where the value of this field is iterated using the
     [`flip` entity](SPEC_ROOT/appendices/entities.md#flip).
-    The data type array provides a value for each volume in a 4D dataset and
-    should only be used when the volume timing is critical for interpretation of
-    the data, such as in
-    [ASL](SPEC_ROOT/modality-specific-files/magnetic-resonance-imaging-data.md#\
-    arterial-spin-labeling-perfusion-data)
-    or variable flip angle fMRI sequences.
   anyOf:
     - type: number
       unit: degree
@@ -1875,6 +1957,7 @@ MRAcquisitionType:
     Corresponds to DICOM Tag 0018, 0023 `MR Acquisition Type`.
   type: string
   enum:
+    - $ref: objects.enums.OneD.value
     - $ref: objects.enums.TwoD.value
     - $ref: objects.enums.ThreeD.value
 MRTransmitCoilSequence:
@@ -1980,6 +2063,19 @@ MatrixCoilMode:
     There are typically different default modes when using un-accelerated or
     accelerated (for example, `"GRAPPA"`, `"SENSE"`) imaging.
   type: string
+MatrixSize:
+  name: MatrixSize
+  display_name: Matrix Size
+  description: |
+    An array of integers with a length of 3 denoting the matrix size of the acquisition slab.
+    This should be specified as, for example, `[32, 32, 1]` for a 2D acquisition
+    or `[32, 1, 1]` for a 1D acquisition.
+  type: array
+  minItems: 3
+  maxItems: 3
+  items:
+    type: integer
+    minimum: 1
 MaxMovement:
   name: MaxMovement
   display_name: Max Movement
@@ -2044,7 +2140,8 @@ MixingTime:
   name: MixingTime
   display_name: Mixing Time
   description: |
-    In the context of a stimulated- and spin-echo 3D EPI sequence for B1+ mapping,
+    In the context of a stimulated- and spin-echo 3D EPI sequence for B1+ mapping
+    or a stimulated-echo MRS sequence,
     corresponds to the interval between spin- and stimulated-echo pulses.
     In the context of a diffusion-weighted double spin-echo sequence,
     corresponds to the interval between two successive diffusion sensitizing
@@ -2199,6 +2296,19 @@ NonlinearGradientCorrection:
     Boolean stating if the image saved has been corrected for gradient
     nonlinearities by the scanner sequence.
   type: boolean
+NumberOfSpectralPoints:
+  name: NumberOfSpectralPoints
+  display_name: Number Of Spectral Points
+  description: |
+    The number of complex data points in each recorded transient of the detected time-domain MR
+    signal, equivalent to the number of points in a single spectrum.
+  type: integer
+NumberOfTransients:
+  name: NumberOfTransients
+  display_name: Number Of Transients
+  description: |
+    The number of single applications of the pulse sequence recorded during an MRS acquisition.
+  type: integer
 NumberOfVolumesDiscardedByScanner:
   name: NumberOfVolumesDiscardedByScanner
   display_name: Number Of Volumes Discarded By Scanner
@@ -2287,6 +2397,12 @@ OtherAcquisitionParameters:
   description: |
     Description of other relevant image acquisition parameters.
   type: string
+OuterVolumeSuppression:
+  name: OuterVolumeSuppression
+  display_name: Outer-Volume Suppression
+  description: |
+    Boolean indicating whether outer-volume suppression was used prior to acquisition.
+  type: boolean
 PASLType:
   name: PASLType
   display_name: PASL Type
@@ -2536,13 +2652,34 @@ PulseSequenceDetails:
     `"Siemens WIP ### version #.##,"` or
     `"Sequence written by X using a version compiled on MM/DD/YYYY"`).
   type: string
+PulseSequencePulses:
+  name: PulseSequencePulses
+  display_name: Pulse Sequence Pulses
+  description: |
+    The list of pulses used in the pulse sequence.
+    If this field is specified, the array size MUST equal the array size of `"PulseSequenceTiming"`.
+    The strings MAY be of the format `<pulse_name>_R<time-bandwidth_product>`.
+    For example, a sLASER sequence may be described as such:
+    `["P10_R6", "HS4_R25", "HS4_R25", "HS4_R25", "HS4_R25"]`.
+  type: array
+  items:
+    type: string
+PulseSequenceTiming:
+  name: PulseSequenceTiming
+  display_name: Pulse Sequence Timing
+  description: |
+    The time when each RF pulse of the pulse sequence was played out relative to
+    the beginning of the pulse sequence (that is, the top of the excitation RF pulse),
+    specified in seconds.
+  type: array
+  items:
+    type: number
+    unit: s
 PulseSequenceType:
   name: PulseSequenceType
   display_name: Pulse Sequence Type
   description: |
-    A general description of the pulse sequence used for the scan
-    (for example, `"MPRAGE"`, `"Gradient Echo EPI"`, `"Spin Echo EPI"`,
-    `"Multiband gradient echo EPI"`).
+    A general description of the pulse sequence used for the scan.
   type: string
 Purity:
   name: Purity
@@ -2591,6 +2728,18 @@ ReceiveCoilName:
     in which case this field can be derived from an appropriate
     private DICOM field.
   type: string
+ReceiveGain:
+  name: ReceiveGain
+  display_name: Receive Gain
+  description: |
+    The gain of the receive coil.
+  anyOf:
+    - type: number
+      unit: dB
+    - type: array
+      items:
+        type: number
+        unit: dB
 ReconFilterSize:
   name: ReconFilterSize
   display_name: Recon Filter Size
@@ -2679,6 +2828,20 @@ ReferencesAndLinks:
   items:
     type: string
   type: array
+ReferenceSignal:
+  name: ReferenceSignal
+  display_name: Reference Signal
+  description: |
+    The path(s) to the MRS reference file(s), if present, to which the associated
+    MRS data file corresponds.
+    Contains one or more [BIDS URIs](SPEC_ROOT/common-principles.md#bids-uri).
+  anyOf:
+    - type: string
+      format: bids_uri
+    - type: array
+      items:
+        type: string
+        format: bids_uri
 RepetitionTime:
   name: RepetitionTime
   display_name: Repetition Time
@@ -2757,6 +2920,17 @@ Resolution:
     - type: object
       additionalProperties:
         type: string
+ResonantNucleus:
+  name: ResonantNucleus
+  display_name: Resonant Nucleus
+  description: |
+    The isotope of interest of an MR experiment (for example, `"1H"`, `"13C"`, `"31P"`).
+    For multi-nuclei experiments such as <sup>1</sup>H-[<sup>13</sup>C] MR,
+    an array can be used: `["1H", "13C"]`.
+    Corresponds to DICOM Tag 0018, 9100 `Resonant Nucleus`.
+  type: array
+  items:
+    type: string
 RotationOrder:
   name: RotationOrder
   display_name: RotationOrder
@@ -2966,6 +3140,16 @@ ScanningSequence:
     - type: array
       items:
         type: string
+ScanningSequence__mrs:
+  name: ScanningSequence
+  display_name: Scanning Sequence
+  description: |
+    Description of the type of data acquired.
+  type: string
+  enum:
+    - SVS
+    - MRSI
+    - Unlocalized MRS
 ScatterFraction:
   name: ScatterFraction
   display_name: Scatter Fraction
@@ -3287,6 +3471,27 @@ SpecificRadioactivityUnits:
     - type: string
       enum:
         - n/a
+SpectralWidth:
+  name: SpectralWidth
+  display_name: Spectral Width
+  description: |
+    The spectral bandwidth of the MR signal that is sampled, specified in Hz.
+    Corresponds to DICOM Tag 0018, 9052 `Spectral Width`.
+  type: number
+  unit: Hz
+SpectrometerFrequency:
+  name: SpectrometerFrequency
+  display_name: Spectrometer Frequency
+  description: |
+    The frequency of the spectrometer, specified in MHz.
+    For example, this could be `127.764` for a 3T scanner tuned
+    to the resonant frequency of <sup>1</sup>H.
+    For multi-nuclei experiments such as <sup>1</sup>H-[<sup>13</sup>C] MR at 3T,
+    an array can be used: `[127.731, 32.125]`.
+  type: array
+  items:
+    type: number
+    unit: MHz
 SpoilingGradientDuration:
   name: SpoilingGradientDuration
   display_name: Spoiling Gradient Duration
@@ -3606,6 +3811,27 @@ VascularCrushingVENC:
       items:
         type: number
         unit: cm/s
+VolumeAffineMatrix:
+  name: VolumeAffineMatrix
+  display_name: Volume Affine Matrix
+  description: |
+    A 4-by-4 matrix using identical conventions and coordinate system to
+    the *{qs}form* NIfTI affine matrix to define the orientation,
+    position, and size of an additional VOI.
+    This VOI defines a spatial region in addition to the primary method of localization
+    (encoded in the NIfTI header *{qs}form*).
+    Typically not defined for data stored with a single spatial voxel or FID-MRSI.
+    For example: `[[30, 0, 0, -30], [0, 30, -2.27, -72.67], [0, 2.27, 29.91, 5.47],
+    [0, 0, 0, 1]]`.
+  type: array
+  minItems: 4
+  maxItems: 4
+  items:
+    type: array
+    minItems: 4
+    maxItems: 4
+    items:
+      type: number
 VELChannelCount:
   name: VELChannelCount
   display_name: Velocity Channel Count
@@ -3626,12 +3852,10 @@ VolumeTiming:
   description: |
     The time at which each volume was acquired during the acquisition.
     It is described using a list of times referring to the onset of each volume
-    in the BOLD series.
-    The list must have the same length as the BOLD series,
+    in the series.
+    The list must have the same length as the series,
     and the values must be non-negative and monotonically increasing.
-    This field is mutually exclusive with `"RepetitionTime"` and `"DelayTime"`.
-    If defined, this requires acquisition time (TA) be defined via either
-    `"SliceTiming"` or `"AcquisitionDuration"` be defined.
+    This field is mutually exclusive with `"RepetitionTime"`.
   type: array
   minItems: 1
   items:
diff --git a/src/schema/objects/modalities.yaml b/src/schema/objects/modalities.yaml
index 4809e380df..b80c73d0e1 100644
--- a/src/schema/objects/modalities.yaml
+++ b/src/schema/objects/modalities.yaml
@@ -35,3 +35,6 @@ motion:
 nirs:
   display_name: Near-Infrared Spectroscopy
   description: Data acquired with NIRS.
+mrs:
+  display_name: Magnetic Resonance Spectroscopy
+  description: Data acquired with MRS.
diff --git a/src/schema/objects/suffixes.yaml b/src/schema/objects/suffixes.yaml
index b370ef646a..93cd15afa3 100644
--- a/src/schema/objects/suffixes.yaml
+++ b/src/schema/objects/suffixes.yaml
@@ -693,6 +693,18 @@ motion:
   display_name: Motion
   description: |
     Data recorded from a tracking system store.
+mrsi:
+  value: mrsi
+  display_name: Magnetic resonance spectroscopy imaging
+  description: |
+    MRS acquisitions where additional imaging gradients are used
+    to detect the MR signal from 1, 2, or 3 spatial dimensions.
+mrsref:
+  value: mrsref
+  display_name: MRS reference acquisition
+  description: |
+    An MRS acquisition collected to serve as a concentration reference for absolute quantification
+    or as a calibration reference for preprocessing (for example, eddy-current correction).
 nirs:
   value: nirs
   display_name: Near Infrared Spectroscopy
@@ -819,8 +831,19 @@ stim:
   display_name: Continuous recording
   description: |
     Continuous measures, such as parameters of a film or audio stimulus.
+svs:
+  value: svs
+  display_name: Single-voxel spectroscopy
+  description: |
+    MRS acquisitions where the detected MR signal is spatially localized to a single volume.
 uCT:
   value: uCT
   display_name: Micro-CT
   description: |
     Micro-CT imaging data
+unloc:
+  value: unloc
+  display_name: Unlocalized spectroscopy
+  description: |
+    MRS acquisitions run without localization.
+    This includes signals detected using coil sensitivity only.
diff --git a/src/schema/rules/checks/mrs.yaml b/src/schema/rules/checks/mrs.yaml
new file mode 100644
index 0000000000..598a59c94f
--- /dev/null
+++ b/src/schema/rules/checks/mrs.yaml
@@ -0,0 +1,29 @@
+---
+MRSNiftiConsistency:
+  issue:
+    code: MRS_NIFTI_CONSISTENCY
+    message: |
+      ResonantNucleus and/or SpectrometerFrequency fields are inconsistent
+      between the NIfTI-MRS header extension and the BIDS sidecar.
+    level: error
+  selectors:
+    - datatype == "mrs"
+    - type(nifti_header.mrs) != "null"
+  checks:
+    - sidecar.ResonantNucleus == nifti_header.mrs.ResonantNucleus
+    - sidecar.SpectrometerFrequency == nifti_header.mrs.SpectrometerFrequency
+
+MRSMatrixSize:
+  issue:
+    code: MRS_MATRIX_SIZE
+    message: |
+      MatrixSize metadata must match NIfTI header field `dim[1:4]`.
+    level: error
+  selectors:
+    - datatype == "mrs"
+    - type(nifti_header) != "null"
+    - type(sidecar.MatrixSize) != "null"
+  checks:
+    - sidecar.MatrixSize[0] == nifti_header.dim[1]
+    - sidecar.MatrixSize[1] == nifti_header.dim[2]
+    - sidecar.MatrixSize[2] == nifti_header.dim[3]
diff --git a/src/schema/rules/entities.yaml b/src/schema/rules/entities.yaml
index 2194a61a92..44174d333e 100644
--- a/src/schema/rules/entities.yaml
+++ b/src/schema/rules/entities.yaml
@@ -7,6 +7,8 @@
 - task
 - tracksys
 - acquisition
+- nucleus
+- volume
 - ceagent
 - tracer
 - stain
diff --git a/src/schema/rules/files/raw/mrs.yaml b/src/schema/rules/files/raw/mrs.yaml
new file mode 100644
index 0000000000..fe95f08f3a
--- /dev/null
+++ b/src/schema/rules/files/raw/mrs.yaml
@@ -0,0 +1,24 @@
+---
+mrs:
+  suffixes:
+    - svs
+    - mrsi
+    - unloc
+    - mrsref
+  extensions:
+    - .nii.gz
+    - .nii
+    - .json
+  datatypes:
+    - mrs
+  entities:
+    subject: required
+    session: optional
+    task: optional
+    acquisition: optional
+    reconstruction: optional
+    run: optional
+    echo: optional
+    inversion: optional
+    nucleus: optional
+    volume: optional
diff --git a/src/schema/rules/files/raw/task.yaml b/src/schema/rules/files/raw/task.yaml
index b7171e568f..812765a063 100644
--- a/src/schema/rules/files/raw/task.yaml
+++ b/src/schema/rules/files/raw/task.yaml
@@ -91,6 +91,16 @@ events__pet:
     reconstruction: optional
     run: optional
 
+events__mrs:
+  $ref: rules.files.raw.task.events
+  datatypes:
+    - mrs
+  entities:
+    $ref: rules.files.raw.task.events.entities
+    reconstruction: optional
+    nucleus: optional
+    volume: optional
+
 timeseries__func:
   $ref: rules.files.raw.task.timeseries
   datatypes:
diff --git a/src/schema/rules/modalities.yaml b/src/schema/rules/modalities.yaml
index 2f290ca014..ccba1c3ef1 100644
--- a/src/schema/rules/modalities.yaml
+++ b/src/schema/rules/modalities.yaml
@@ -31,3 +31,6 @@ motion:
 nirs:
   datatypes:
     - nirs
+mrs:
+  datatypes:
+    - mrs
diff --git a/src/schema/rules/sidecars/func.yaml b/src/schema/rules/sidecars/func.yaml
index 12a2b01e35..67ec04e84f 100644
--- a/src/schema/rules/sidecars/func.yaml
+++ b/src/schema/rules/sidecars/func.yaml
@@ -41,6 +41,10 @@ MRIFuncVolumeTiming:
     VolumeTiming:
       level: required
       level_addendum: mutually exclusive with `RepetitionTime`
+      description_addendum: |
+        This field is mutually exclusive with `"DelayTime"`.
+        If defined, this requires acquisition time (TA) be defined via either
+        `"SliceTiming"` or `"AcquisitionDuration"`.
 
 # Timing Parameters
 MRIFuncTimingParameters:
diff --git a/src/schema/rules/sidecars/mri.yaml b/src/schema/rules/sidecars/mri.yaml
index ccfb4e0737..d57a053bec 100644
--- a/src/schema/rules/sidecars/mri.yaml
+++ b/src/schema/rules/sidecars/mri.yaml
@@ -80,8 +80,14 @@ MRISequenceSpecifics:
     - modality == "mri"
     - match(extension, "^\.nii(\.gz)?$")
   fields:
-    PulseSequenceType: recommended
-    ScanningSequence: recommended
+    PulseSequenceType:
+      level: recommended
+      description_addendum: |
+        For example, `"MPRAGE"`, `"Gradient Echo EPI"`, `"Spin Echo EPI"`, `"Multiband gradient
+        echo EPI"`.
+    ScanningSequence:
+      level: recommended
+      description_addendum: Corresponds to DICOM Tag 0018, 0020 `Scanning Sequence`.
     SequenceVariant: recommended
     ScanOptions: recommended
     SequenceName: recommended
@@ -216,6 +222,13 @@ MRITimingParameters:
       level_addendum: |
         required if corresponding fieldmap data is present,
         or the data comes from a multi-echo sequence or Arterial Spin Labeling.
+      description_addendum: |
+        The data type array provides a value for each volume in a 4D dataset and
+        should only be used when the volume timing is critical for interpretation
+        of the data, such as in
+        [ASL](SPEC_ROOT/modality-specific-files/magnetic-resonance-imaging-data.md#\
+        arterial-spin-labeling-perfusion-data)
+        or variable echo time fMRI sequences.
     InversionTime: recommended
     DwellTime: recommended
 
@@ -279,6 +292,13 @@ MRIFlipAngleLookLockerFalse:
     FlipAngle:
       level: recommended
       level_addendum: required if LookLocker is set to `true`
+      description_addendum: |
+        The data type array provides a value for each volume in a 4D dataset and
+        should only be used when the volume timing is critical for interpretation of
+        the data, such as in
+        [ASL](SPEC_ROOT/modality-specific-files/magnetic-resonance-imaging-data.md#\
+        arterial-spin-labeling-perfusion-data)
+        or variable flip angle fMRI sequences.
 
 MRIFlipAngleLookLockerTrue:
   selectors:
@@ -287,6 +307,13 @@ MRIFlipAngleLookLockerTrue:
   fields:
     FlipAngle:
       level: required
+      description_addendum: |
+        The data type array provides a value for each volume in a 4D dataset and
+        should only be used when the volume timing is critical for interpretation of
+        the data, such as in
+        [ASL](SPEC_ROOT/modality-specific-files/magnetic-resonance-imaging-data.md#\
+        arterial-spin-labeling-perfusion-data)
+        or variable flip angle fMRI sequences.
       issue:
         code: LOOK_LOCKER_FLIP_ANGLE_MISSING
         message: |
diff --git a/src/schema/rules/sidecars/mrs.yaml b/src/schema/rules/sidecars/mrs.yaml
new file mode 100644
index 0000000000..28796eb5e4
--- /dev/null
+++ b/src/schema/rules/sidecars/mrs.yaml
@@ -0,0 +1,175 @@
+#
+# Groups of related metadata fields
+#
+# Assumptions: never need disjunction of selectors
+# Assumptions: top-to-bottom overrides is sufficient logic
+
+---
+# MRS Common metadata fields
+MRSScannerHardware:
+  selectors:
+    - modality == "mrs"
+    - match(extension, "^\.nii(\.gz)?$")
+  fields:
+    InstitutionName: recommended
+    InstitutionAddress: recommended
+    InstitutionalDepartmentName: recommended
+    Manufacturer: recommended
+    ManufacturersModelName: recommended
+    DeviceSerialNumber: recommended
+    StationName: recommended
+    SoftwareVersions: recommended
+    MagneticFieldStrength: recommended
+    ReceiveCoilName: recommended
+    ReceiveCoilActiveElements: recommended
+    NumberReceiveCoilActiveElements: optional
+    NumberTransmitCoilActiveElements: optional
+
+MRSSample:
+  selectors:
+    - modality == "mrs"
+    - match(extension, "^\.nii(\.gz)?$")
+  fields:
+    BodyPart:
+      level: optional
+      level_addendum: required if `voi` entity is present
+      description_addendum: Corresponds to DICOM Tag 0018, 0015 `Body Part Examined`.
+    BodyPartDetails:
+      level: optional
+      level_addendum: required if `voi` entity is present
+    BodyPartDetailsOntology: optional
+
+MRSSampleVOI:
+  selectors:
+    - modality == "mrs"
+    - match(extension, "^\.nii(\.gz)?$")
+    - '"volume" in entities'
+  fields:
+    BodyPart: required
+    BodyPartDetails: required
+
+MRSSequenceSpecifics:
+  selectors:
+    - modality == "mrs"
+    - match(extension, "^\.nii(\.gz)?$")
+  fields:
+    PulseSequenceType:
+      level: recommended
+      description_addendum: |
+        For example, `"sLASER"`, `"MEGA-PRESS"`, `"EPSI"`, `"Metabolite-cycled MRSI"`.
+    ScanningSequence__mrs: recommended
+    SequenceName: recommended
+    PulseSequenceDetails: recommended
+    WaterSuppression: recommended
+    WaterSuppressionTechnique: optional
+    OuterVolumeSuppression: optional
+    B0ShimmingTechnique: optional
+    B1ShimmingTechnique: optional
+
+MRSRequiredFields:
+  selectors:
+    - modality == "mrs"
+    - match(extension, "^\.nii(\.gz)?$")
+  fields:
+    ResonantNucleus: required
+    SpectrometerFrequency: required
+    SpectralWidth: required
+    EchoTime: required
+
+MRSRecommendedFields:
+  selectors:
+    - modality == "mrs"
+    - match(extension, "^\.nii(\.gz)?$")
+  fields:
+    NumberOfSpectralPoints: recommended
+    MixingTime: recommended
+    FlipAngle: recommended
+    AcquisitionVoxelSize: recommended
+    ReferenceSignal: recommended
+
+MRSRepetitionTime:
+  selectors:
+    - modality == "mrs"
+    - match(extension, "^\.nii(\.gz)?$")
+    - '!("VolumeTiming" in sidecar)'
+  fields:
+    RepetitionTime:
+      level: recommended
+      level_addendum: mutually exclusive with `VolumeTiming`
+
+MRSVolumeTiming:
+  selectors:
+    - modality == "mrs"
+    - match(extension, "^\.nii(\.gz)?$")
+    - '!("RepetitionTime" in sidecar)'
+  fields:
+    VolumeTiming:
+      level: recommended
+      level_addendum: mutually exclusive with `RepetitionTime`
+
+MRSConditionalInversionTime:
+  selectors:
+    - modality == "mrs"
+    - match(extension, "^\.nii(\.gz)?$")
+    - entities.inversion
+  fields:
+    InversionTime:
+      level: recommended
+      level_addendum: if `inv` entity is present
+
+MRSConditionalAnatomicalImage:
+  selectors:
+    - modality == "mrs"
+    - match(extension, "^\.nii(\.gz)?$")
+    - intersects(dataset.datatypes, ["anat"])
+  fields:
+    AnatomicalImage:
+      level: recommended
+      level_addendum: if anatomical MRI data are present
+
+MRSConditionalNumTransients:
+  selectors:
+    - modality == "mrs"
+    - match(extension, "^\.nii(\.gz)?$")
+    - intersects([suffix], ["svs", "unloc"])
+  fields:
+    NumberOfTransients:
+      level: recommended
+      level_addendum: for SVS and unlocalized acquisitions
+
+MRSIRecommendedFields:
+  selectors:
+    - modality == "mrs"
+    - match(extension, "^\.nii(\.gz)?$")
+    - suffix == "mrsi"
+  fields:
+    MRAcquisitionType:
+      level: recommended
+      level_addendum: for MRSI
+    MatrixSize:
+      level: recommended
+      level_addendum: for MRSI
+    VolumeAffineMatrix:
+      level: recommended
+      level_addendum: for MRSI
+    EncodingTechnique:
+      level: recommended
+      level_addendum: for MRSI
+
+MRSOptionalFields:
+  selectors:
+    - modality == "mrs"
+    - match(extension, "^\.nii(\.gz)?$")
+  fields:
+    ChemicalShiftOffset: optional
+    ChemicalShiftReference: optional
+    EditTarget: optional
+    EditPulse: optional
+    EditCondition: optional
+    EchoAcquisition: optional
+    ParallelReductionFactorInPlane: optional
+    ParallelAcquisitionTechnique: optional
+    MultibandAccelerationFactor: optional
+    PulseSequenceTiming: optional
+    PulseSequencePulses: optional
+    ReceiveGain: optional