diff --git a/.gitignore b/.gitignore
index 2c988749..9b00e7b3 100644
--- a/.gitignore
+++ b/.gitignore
@@ -11,6 +11,5 @@ MANIFEST
 .coverage
 coverage
 htmlcov
-_trial_temp
+_trial_temp*
 .tox
-_trial_temp.lock
diff --git a/.readthedocs.yml b/.readthedocs.yml
index f0b6cf2e..f7e6d592 100644
--- a/.readthedocs.yml
+++ b/.readthedocs.yml
@@ -1,5 +1,17 @@
+# https://docs.readthedocs.io/en/stable/config-file/v2.html
+version: 2
+
+sphinx:
+  fail_on_warning: false
+
+formats:
+  - pdf
+  - epub
+
 python:
-  version: 2.7
-  pip_install: true
-  extra_requirements:
-    - dev
+  version: 3.8
+  install:
+    - method: pip
+      path: .
+      extra_requirements:
+        - docs
diff --git a/CONTRIBUTING.rst b/CONTRIBUTING.rst
index 046b400d..6bac9978 100644
--- a/CONTRIBUTING.rst
+++ b/CONTRIBUTING.rst
@@ -1,28 +1,24 @@
 Developing
 ==========
 
-Install dependencies:
+This project uses `Tox <https://tox.readthedocs.io/en/latest/config.html>`_ to manage virtual environments.
 
-::
+To run the tests::
 
-    pip install treq[dev]
+    tox -e py38-twisted_latest
 
-Run Tests (unit & integration):
+Lint::
 
-::
-
-    trial treq
-
-Lint:
-
-::
-
-    pep8 treq
-    pyflakes treq
+    tox -e flake8
 
 Build docs::
 
     tox -e docs
+    firefox docs/html/index.html
+
+To do it all::
+
+    tox -p
 
 Release notes
 -------------
diff --git a/changelog.d/296.doc.rst b/changelog.d/296.doc.rst
new file mode 100644
index 00000000..f6606919
--- /dev/null
+++ b/changelog.d/296.doc.rst
@@ -0,0 +1 @@
+The dependency on Sphinx required to build the documentation has been moved from the ``dev`` extra to the new ``docs`` extra.
diff --git a/setup.py b/setup.py
index 3c3ca287..b8ad149a 100644
--- a/setup.py
+++ b/setup.py
@@ -38,9 +38,11 @@
             "dev": [
                 "pep8",
                 "pyflakes",
-                "sphinx",
                 "httpbin==0.5.0",
             ],
+            "docs": [
+                "sphinx>=1.4.8",
+            ],
         },
         package_data={"treq": ["_version"]},
         author="David Reid",
diff --git a/tox.ini b/tox.ini
index 4abd3119..530d8be0 100644
--- a/tox.ini
+++ b/tox.ini
@@ -13,8 +13,6 @@ deps =
     twisted_lowest: Twisted==18.7.0
     twisted_latest: Twisted
     twisted_trunk: https://github.com/twisted/twisted/archive/trunk.zip
-
-    docs: Sphinx>=1.4.8
 setenv =
     # Avoid unnecessary network access when creating virtualenvs for speed.
     VIRTUALENV_NO_DOWNLOAD=1
@@ -53,6 +51,7 @@ commands =
     check-manifest
 
 [testenv:docs]
+extras = docs
 changedir = docs
 commands =
     sphinx-build -b html . html