diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
index bd9d1772..8190a5a1 100644
--- a/.github/workflows/ci.yaml
+++ b/.github/workflows/ci.yaml
@@ -25,27 +25,13 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-latest, macOS-latest]
-        python-version: ["2.7", "3.6", "3.7", "3.8", "3.9", "3.10", "3.11"]
-        gromacs-version: ["2021.1"]
+        os: [ubuntu-latest]
+        python-version: ["3.8", "3.9", "3.10", "3.11"]
+        gromacs-version: ["2023.1"]
         # Test other GROMACS versions selectively on a recent Python.
         # On macOS only test one GROMACS version and two Python versions
         # to keep the testing matrix manageable.
-        exclude:
-          - os: macOS-latest
-            python-version: "3.6"
-          - os: macOS-latest
-            python-version: "3.7"
-          - os: macOS-latest
-            python-version: "3.8"
-          - os: macOS-latest
-            python-version: "3.9"
-          - os: macOS-latest
-            python-version: "3.10"
         include:
-          - os: ubuntu-latest
-            python-version: "2.7"
-            gromacs-version: "4.6.5"    
           - os: ubuntu-latest
             python-version: "3.11"
             gromacs-version: "4.6.5"
@@ -60,10 +46,18 @@ jobs:
             gromacs-version: "2020.6"
           - os: ubuntu-latest
             python-version: "3.11"
-            gromacs-version: "2022.4"
+            gromacs-version: "2021.1"       
           - os: ubuntu-latest
             python-version: "3.11"
-            gromacs-version: "2023.1"
+            gromacs-version: "2022.4"
+          # explicitly include a few macOS runners
+          # (conda-forge GROMACS >= 2021 is compiled to use rdtscp CPU instruction but these
+          # are not available in the macOS GitHub runner so we need to use a different GROMACS
+          # version. Try 2018.5 from bioconda. (2021.5 worked previously but not anymore.)
+          # Locally 2023.1 was successfully tested on Intel macOS 13.5.)
+          - os: macOS-latest
+            python-version: "3.11"
+            gromacs-version: "2018.6"
             
 
     env:
@@ -95,6 +89,7 @@ jobs:
       run: |
          micromamba info
          micromamba list
+         cat /proc/cpuinfo || (/usr/sbin/system_profiler SPHardwareDataType; /usr/sbin/sysctl -a | grep machdep.cpu)
 
     - name: Install pytest and plugins
       run: |
@@ -103,7 +98,6 @@ jobs:
     - name: Install GROMACS (${{ matrix.gromacs-version }})
       # UGLY HACK/FIX (probably to issues with bioconda packages)
       # - For 3.9, micromamba insists on using pypy 3.9 (and --py-pin does not help).
-      # - For 2.7 macOS, numkit would get uninstalled.
       # We can't freeze because then it's not possible to install older GROMACS versions from bioconda. 
       run: |
          micromamba install 'gromacs==${{ matrix.gromacs-version }}' pocl numkit python=${{ matrix.python-version }}.*=*_cpython
diff --git a/CHANGES b/CHANGES
index b8323e83..2b685dcd 100644
--- a/CHANGES
+++ b/CHANGES
@@ -2,6 +2,12 @@
  CHANGELOG for GromacsWrapper
 ==============================
 
+2023-xx-xx      0.9.0
+orbeckst
+
+* removed support for legacy Python (<= 3.7) (#259)
+
+
 2023-09-16      0.8.5
 orbeckst
 
diff --git a/README.rst b/README.rst
index 92200f0e..65181b0d 100644
--- a/README.rst
+++ b/README.rst
@@ -11,8 +11,8 @@
 
 A primitive Python wrapper around the Gromacs_ tools. The library is
 tested with GROMACS 4.6.5, 2018.x, 2019.x, 2020.x, 2021.x, 2022.x,
-2023.x (and 5.x and 2016.x should also work). It supports Python 2.7
-and 3.6--3.11 on Linux and macOS.
+2023.x (and 5.x and 2016.x should also work). It supports Python
+3.8--3.11 on Linux and macOS.
 
 GromacsWrapper also provides a small library (cook book) of often-used
 recipes and helper functions to set up MD simulations.
diff --git a/doc/sphinx/source/installation.txt b/doc/sphinx/source/installation.txt
index 83aed698..85b826e8 100644
--- a/doc/sphinx/source/installation.txt
+++ b/doc/sphinx/source/installation.txt
@@ -6,7 +6,6 @@
  Installation
 ==============
 
-
 This document should help you to install the **GromacsWrapper**
 package. Please raise and issue in the `Issue Tracker`_ if problems
 occur or if you have suggestions on how to improve the package or
@@ -103,19 +102,17 @@ formatting so please install black_ and run it on your code.
 Requirements
 ============
 
-Python_ 2.7.x or Python >= 3.6 and GROMACS_ (4.6.x, 2016, 2018, 2019,
-2020, 2021, 2022) must be installed. ipython_ is very much
-recommended.
+Python_ >= 3.8 and GROMACS_ (4.6.x, 2016, 2018, 2019, 2020, 2021,
+2022, 2023) must be installed.
 
 .. _Python: http://www.python.org
-.. _ipython: http://ipython.scipy.org
 
 
 System requirements
 -------------------
 
-Tested with Python 2.7.x and Python 3.6--3.11 on Linux and Mac
-OS X. Earlier Python versions are not supported.
+Tested with Python 3.8--3.11 on Linux and Mac OS X. Earlier Python
+versions were only supported until release 0.8.5.
 
 
 Required Python modules
diff --git a/gromacs/__init__.py b/gromacs/__init__.py
index f73e0d09..65353f4a 100644
--- a/gromacs/__init__.py
+++ b/gromacs/__init__.py
@@ -169,8 +169,6 @@
 .. autodata:: __version__
 
 """
-from __future__ import absolute_import
-
 __docformat__ = "restructuredtext en"
 
 import os
diff --git a/gromacs/cbook.py b/gromacs/cbook.py
index 9be86fa1..4b56a3e6 100644
--- a/gromacs/cbook.py
+++ b/gromacs/cbook.py
@@ -125,8 +125,6 @@
 # new class and set arguments explicitly in init (using kwargs['flag'] =
 # default) ... or I can write some meta(??) class to do this nicely
 
-from __future__ import absolute_import, with_statement
-
 __docformat__ = "restructuredtext en"
 
 import sys
@@ -136,7 +134,6 @@
 import tempfile
 import shutil
 import glob
-import six
 
 import logging
 
diff --git a/gromacs/collections.py b/gromacs/collections.py
index 267b5b76..005a53dc 100644
--- a/gromacs/collections.py
+++ b/gromacs/collections.py
@@ -15,7 +15,7 @@
 """
 
 import os.path
-from six.moves import cPickle
+import pickle
 from numpy import all, any
 
 
@@ -50,10 +50,10 @@ def save(self, filename):
 
         If no extension is provided, ".collection" is appended.
         """
-        cPickle.dump(
+        pickle.dump(
             self,
             open(self._canonicalize(filename), "wb"),
-            protocol=cPickle.HIGHEST_PROTOCOL,
+            protocol=pickle.HIGHEST_PROTOCOL,
         )
 
     def load(self, filename, append=False):
@@ -64,7 +64,7 @@ def load(self, filename, append=False):
 
         If no extension is provided, ".collection" is appended.
         """
-        tmp = cPickle.load(open(self._canonicalize(filename), "rb"))
+        tmp = pickle.load(open(self._canonicalize(filename), "rb"))
         if append:
             self.extend(tmp)
         else:
diff --git a/gromacs/config.py b/gromacs/config.py
index 559c5011..1ebc5dce 100644
--- a/gromacs/config.py
+++ b/gromacs/config.py
@@ -225,43 +225,13 @@
 .. autodata:: qscript_template
 
 """
-from __future__ import absolute_import, with_statement, print_function
-
 import os
 import logging
 import re
 import subprocess
 import sys
 
-if sys.version_info[0] < 3:  # several differences for Python 2
-    from ConfigParser import SafeConfigParser as ConfigParser
-    from ConfigParser import NoSectionError, NoOptionError
-
-    # Define read_file to point to the (deprecated in Python 3) readfp
-    # in order to have consistent, non-deprecated syntax
-    ConfigParser.read_file = ConfigParser.readfp
-
-    # Implement the new `fallback` kwarg based on the Python 3.7 implementation
-    # https://github.com/python/cpython/blob/3.7/Lib/configparser.py#L804
-    # This should ensure backwards compatibility.
-    _cf_getbool = ConfigParser.getboolean
-    _UNSET = object()
-
-    def _getboolean(self, section, option, fallback=_UNSET, **kwargs):
-        """Return a boolean for the specified config option
-
-        If *fallback* is used, it will be returned if there if the
-        option is not specified anywhere (defaults, config file)."""
-        try:  # Try using the Python 2 function
-            return _cf_getbool(self, section, option, **kwargs)
-        except (NoSectionError, NoOptionError):
-            if fallback is _UNSET:
-                raise
-        return fallback  # If fallback is given, use that value
-
-    ConfigParser.getboolean = _getboolean
-else:
-    from configparser import ConfigParser
+from configparser import ConfigParser
 
 from pkg_resources import resource_filename, resource_listdir
 
diff --git a/gromacs/core.py b/gromacs/core.py
index 57674255..3af1e055 100644
--- a/gromacs/core.py
+++ b/gromacs/core.py
@@ -98,9 +98,6 @@
 .. autoclass:: PopenWithInput
    :members:
 """
-from __future__ import absolute_import, with_statement, print_function
-import six
-
 __docformat__ = "restructuredtext en"
 
 import sys
@@ -277,13 +274,13 @@ def Popen(self, *args, **kwargs):
         use_shell = kwargs.pop("use_shell", False)
         if input:
             stdin = PIPE
-            if isinstance(input, six.string_types) and not input.endswith("\n"):
+            if isinstance(input, str) and not input.endswith("\n"):
                 # make sure that input is a simple string with \n line endings
-                input = six.text_type(input) + "\n"
+                input = str(input) + "\n"
             else:
                 try:
                     # make sure that input is a simple string with \n line endings
-                    input = "\n".join(map(six.text_type, input)) + "\n"
+                    input = "\n".join(map(str, input)) + "\n"
                 except TypeError:
                     # so maybe we are a file or something ... and hope for the best
                     pass
@@ -733,9 +730,6 @@ def __init__(self, *args, **kwargs):
         """
         kwargs.setdefault("close_fds", True)  # fixes 'Too many open fds' with 2.6
         self.input = kwargs.pop("input", None)
-        if six.PY2 and self.input is not None:
-            # in Python 2, subprocess.Popen uses os.write(chunk) with default ASCII encoding
-            self.input = self.input.encode("utf-8")
         self.command = args[0]
         try:
             input_string = (
diff --git a/gromacs/environment.py b/gromacs/environment.py
index 08f23069..fa5995f4 100644
--- a/gromacs/environment.py
+++ b/gromacs/environment.py
@@ -36,7 +36,6 @@
    :members:
 
 """
-import six
 
 
 # set up flags for core routines (more convoluted than strictly necessary but should
@@ -87,7 +86,7 @@ def __setitem__(self, name, value):
         self.get_flag(name).set(value)
 
     def _itervalues(self):
-        return six.itervalues(super(Flags, self))
+        return super(Flags, self).values()
 
     def _items(self):
         return super(Flags, self).items()
diff --git a/gromacs/fileformats/__init__.py b/gromacs/fileformats/__init__.py
index e4806b2a..7a79604a 100644
--- a/gromacs/fileformats/__init__.py
+++ b/gromacs/fileformats/__init__.py
@@ -4,7 +4,6 @@
 # See the file COPYING for details.
 
 # file formats
-from __future__ import absolute_import
 
 __all__ = ["XVG", "MDP", "NDX", "uniqueNDX", "XPM", "TOP"]
 
diff --git a/gromacs/fileformats/convert.py b/gromacs/fileformats/convert.py
index 3b1dc543..87322db3 100644
--- a/gromacs/fileformats/convert.py
+++ b/gromacs/fileformats/convert.py
@@ -38,7 +38,6 @@
 .. autofunction:: to_unicode
 
 """
-import six
 
 import re
 
@@ -47,17 +46,17 @@ def to_unicode(obj):
     """Convert obj to unicode (if it can be be converted).
 
     Conversion is only attempted if `obj` is a string type (as
-    determined by :data:`six.string_types`).
+    determined by :class:`str`).
 
     .. versionchanged:: 0.7.0
        removed *encoding* keyword argument
 
     """
-    if not isinstance(obj, six.string_types):
+    if not isinstance(obj, str):
         return obj
 
     try:
-        obj = six.text_type(obj)
+        obj = str(obj)
     except TypeError:
         pass
     return obj
diff --git a/gromacs/fileformats/mdp.py b/gromacs/fileformats/mdp.py
index d1a07277..e14a2b94 100644
--- a/gromacs/fileformats/mdp.py
+++ b/gromacs/fileformats/mdp.py
@@ -18,12 +18,9 @@
 """
 
 
-from __future__ import absolute_import, with_statement
-
 import os, errno
 import re
 import warnings
-import six
 import numpy
 
 
@@ -163,7 +160,7 @@ def write(self, filename=None, skipempty=False):
                 else:  # parameter = value
                     if skipempty and (v == "" or v is None):
                         continue
-                    if isinstance(v, six.string_types) or not hasattr(v, "__iter__"):
+                    if isinstance(v, str) or not hasattr(v, "__iter__"):
                         mdp.write("{k!s} = {v!s}\n".format(**vars()))
                     else:
                         mdp.write("{} = {}\n".format(k, " ".join(map(str, v))))
diff --git a/gromacs/fileformats/ndx.py b/gromacs/fileformats/ndx.py
index 69150e27..4356a4f2 100644
--- a/gromacs/fileformats/ndx.py
+++ b/gromacs/fileformats/ndx.py
@@ -23,10 +23,6 @@
 .. autoclass:: IndexSet
 """
 
-from __future__ import absolute_import, with_statement
-
-from six.moves import range
-
 import os, errno
 import re
 import warnings
diff --git a/gromacs/fileformats/top.py b/gromacs/fileformats/top.py
index 7fd0f879..fce89983 100644
--- a/gromacs/fileformats/top.py
+++ b/gromacs/fileformats/top.py
@@ -51,7 +51,6 @@
    Exchange (HREX) simulations. See ``scripts/gw-partial_tempering.py`` for an example.
 
 """
-from __future__ import absolute_import
 
 import textwrap
 import logging
diff --git a/gromacs/fileformats/xpm.py b/gromacs/fileformats/xpm.py
index fd203b84..3386cbb8 100644
--- a/gromacs/fileformats/xpm.py
+++ b/gromacs/fileformats/xpm.py
@@ -69,10 +69,6 @@
 
 """
 
-from __future__ import absolute_import, with_statement
-
-from six.moves import range
-
 import os, errno
 import re
 import warnings
diff --git a/gromacs/fileformats/xvg.py b/gromacs/fileformats/xvg.py
index 9b4cfefa..3e54a9a5 100644
--- a/gromacs/fileformats/xvg.py
+++ b/gromacs/fileformats/xvg.py
@@ -187,9 +187,6 @@
 .. autofunction:: break_array
 
 """
-from __future__ import with_statement, absolute_import
-
-from six.moves import zip, range
 
 import os
 import errno
diff --git a/gromacs/formats.py b/gromacs/formats.py
index d534bb3c..8b952a47 100644
--- a/gromacs/formats.py
+++ b/gromacs/formats.py
@@ -45,8 +45,6 @@
    :members:
 
 """
-from __future__ import absolute_import
-
 __docformat__ = "restructuredtext en"
 
 __all__ = ["XVG", "MDP", "NDX", "uniqueNDX", "XPM", "TOP"]
diff --git a/gromacs/log.py b/gromacs/log.py
index 0337aa9f..1160f0f4 100644
--- a/gromacs/log.py
+++ b/gromacs/log.py
@@ -60,7 +60,6 @@
 .. autogenerated, see Online Docs
 
 """
-from __future__ import absolute_import
 
 import logging
 
diff --git a/gromacs/qsub.py b/gromacs/qsub.py
index 8f722b98..114350ee 100644
--- a/gromacs/qsub.py
+++ b/gromacs/qsub.py
@@ -192,8 +192,6 @@
 .. autodata:: queuing_systems
 
 """
-from __future__ import absolute_import, with_statement
-
 import os
 import errno
 from os.path import relpath
diff --git a/gromacs/run.py b/gromacs/run.py
index 701141c1..af7094c2 100644
--- a/gromacs/run.py
+++ b/gromacs/run.py
@@ -96,8 +96,6 @@ class MDrunnerMPI(gromacs.run.MDrunner):
 .. autofunction:: find_gromacs_command
 
 """
-from __future__ import absolute_import, with_statement
-
 __docformat__ = "restructuredtext en"
 
 import warnings
diff --git a/gromacs/scaling.py b/gromacs/scaling.py
index a4802221..e61c3394 100644
--- a/gromacs/scaling.py
+++ b/gromacs/scaling.py
@@ -20,8 +20,6 @@
 .. autofunction:: partial_tempering
 
 """
-from __future__ import absolute_import, division, print_function
-
 import math
 import copy
 import logging
diff --git a/gromacs/setup.py b/gromacs/setup.py
index 2beecbc1..55e7e691 100644
--- a/gromacs/setup.py
+++ b/gromacs/setup.py
@@ -114,9 +114,6 @@
 .. autodata:: vdw_lipid_atom_radii
 
 """
-
-from __future__ import absolute_import, with_statement
-
 __docformat__ = "restructuredtext en"
 
 import os
diff --git a/gromacs/tools.py b/gromacs/tools.py
index 11c4b188..ae025b45 100644
--- a/gromacs/tools.py
+++ b/gromacs/tools.py
@@ -188,10 +188,6 @@
 .. The following is autogenerated with sphinx.
 
 """
-from __future__ import absolute_import
-
-import six
-
 import os.path
 import tempfile
 import subprocess
@@ -354,11 +350,7 @@ def run(self, *args, **kwargs):
 
     def _fake_multi_ndx(self, **kwargs):
         ndx = kwargs.get("n")
-        if (
-            not (ndx is None or isinstance(ndx, six.string_types))
-            and len(ndx) > 1
-            and "s" in kwargs
-        ):
+        if not (ndx is None or isinstance(ndx, str)) and len(ndx) > 1 and "s" in kwargs:
             ndx.append(kwargs.get("s"))
             kwargs["n"] = merge_ndx(*ndx)
         return kwargs
@@ -569,7 +561,7 @@ def merge_ndx(*args):
 # with only 5.x
 # update with temporary directory
 for fancy, cmd in list(registry.items()):
-    for c5, c4 in six.iteritems(NAMES5TO4):
+    for c5, c4 in NAMES5TO4.items():
         # have to check each one, since it's possible there are suffixes
         # like for double precision; cmd.command_name is Gromacs name
         # (e.g. 'convert-tpr') so we need to be careful in the processing below.
@@ -679,7 +671,7 @@ def __str__(self):
 
 
 # Append class doc for each command
-for name in six.iterkeys(registry):
+for name in registry.keys():
     __doc__ += ".. class:: {0!s}\n    :noindex:\n".format(name)
 
 registry["Release"] = Release
diff --git a/gromacs/utilities.py b/gromacs/utilities.py
index 097760a9..4f1929de 100644
--- a/gromacs/utilities.py
+++ b/gromacs/utilities.py
@@ -86,14 +86,8 @@ class is derived from it.
 .. autodata:: amino_acid_codes
 
 """
-from __future__ import absolute_import, with_statement, division
-
 __docformat__ = "restructuredtext en"
 
-import six
-from six import string_types
-
-import sys
 import os
 import glob
 import fnmatch
@@ -342,7 +336,7 @@ def _get_stream(filename, openfunction=open, mode="r"):
         # case we have to ignore the error and return None. Second is when openfunction can't open the file because
         # either the file isn't there or the permissions don't allow access.
         if errno.errorcode[err.errno] in ["ENOENT", "EACCES"]:
-            six.reraise(*sys.exc_info())
+            raise
         return None
     if mode.startswith("r"):
         # additional check for reading (eg can we uncompress) --- is this needed?
@@ -724,7 +718,7 @@ def __repr__(self):
 
 def iterable(obj):
     """Returns ``True`` if *obj* can be iterated over and is *not* a  string."""
-    if isinstance(obj, string_types):
+    if isinstance(obj, str):
         return False  # avoid iterating over characters of a string
     if hasattr(obj, "next"):
         return True  # any iterator will do
diff --git a/setup.py b/setup.py
index e3b90cf6..713de0f1 100644
--- a/setup.py
+++ b/setup.py
@@ -4,7 +4,6 @@
 #
 # See the files INSTALL and README for details or visit
 # https://github.com/Becksteinlab/GromacsWrapper
-from __future__ import with_statement
 from setuptools import setup, find_packages
 
 import versioneer
@@ -17,7 +16,7 @@
     name="GromacsWrapper",
     version=versioneer.get_version(),
     cmdclass=versioneer.get_cmdclass(),
-    description="A Python wrapper around the Gromacs tools.",
+    description="A Python wrapper around the GROMACS tools.",
     long_description=long_description,
     long_description_content_type="text/x-rst",
     author="Oliver Beckstein",
@@ -35,12 +34,7 @@
         "Operating System :: POSIX",
         "Operating System :: MacOS :: MacOS X",
         "Operating System :: Microsoft :: Windows ",
-        "Programming Language :: Python",
-        "Programming Language :: Python :: 2",
-        "Programming Language :: Python :: 2.7",
         "Programming Language :: Python :: 3",
-        "Programming Language :: Python :: 3.6",
-        "Programming Language :: Python :: 3.7",
         "Programming Language :: Python :: 3.8",
         "Programming Language :: Python :: 3.9",
         "Programming Language :: Python :: 3.10",
@@ -70,7 +64,6 @@
     },
     install_requires=[
         "numpy>=1.0",
-        "six",  # towards py 3 compatibility
         "numkit",  # numerical helpers
         "matplotlib",
     ],