diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2ac9df712b0..0b467b4715c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,6 @@
 ## Releases
 
-* Unreleased
+* v4.0 (3rd December 2021)
     - Front end improvements:
         - Multi-page form reporting.
         - New aerial map toggle.
diff --git a/README.md b/README.md
index 60472565660..7246ec08478 100644
--- a/README.md
+++ b/README.md
@@ -14,7 +14,7 @@ RSS alerts of problems in their area.
 
 It was created in 2007 by [mySociety](https://www.mysociety.org/) for reporting
 problems to UK councils and has been copied around the world. The FixMyStreet
-Platform is now at version 3.1; see CHANGELOG.md for a version history.
+Platform is now at version 4.0; see CHANGELOG.md for a version history.
 
 ## Installation
 
diff --git a/bin/site-specific-install.sh b/bin/site-specific-install.sh
index ae9497aef96..8da51dc3d28 100644
--- a/bin/site-specific-install.sh
+++ b/bin/site-specific-install.sh
@@ -1,7 +1,7 @@
 #!/bin/sh
 
 # Set this to the version we want to check out
-VERSION=${VERSION_OVERRIDE:-v3.1}
+VERSION=${VERSION_OVERRIDE:-v4.0}
 
 PARENT_SCRIPT_URL=https://github.com/mysociety/commonlib/blob/master/bin/install-site.sh
 
diff --git a/docs/_posts/2021-12-03-v4.0.md b/docs/_posts/2021-12-03-v4.0.md
new file mode 100644
index 00000000000..ea482c4b1bb
--- /dev/null
+++ b/docs/_posts/2021-12-03-v4.0.md
@@ -0,0 +1,72 @@
+---
+layout: post
+title: Version 4.0
+author: matthew
+---
+
+<div class="r" align="right">
+<a data-flickr-embed="true" href="https://www.flickr.com/photos/wwarby/1580431681/" title="Westminster Bridge"><img src="https://live.staticflickr.com/2034/1580431681_388dc2671d.jpg" width="500" height="375" alt="Westminster Bridge"></a><script async src="//embedr.flickr.com/assets/client-code.js" charset="utf-8"></script>
+</div>
+
+Well, 2021 has certainly been a year, hasn’t it. Apologies for the delay
+between releases, but we are now releasing **version 4.0**, with a number of
+new features, outlined below. For those who don't want to update immediately,
+we are also releasing **version 3.1.1** as an update to 3.1 including a number
+of bugfixes and the update necessary to deal with issues caused by the rollover
+of the Let’s Encrypt root certificate.
+
+### Multi-page reporting form
+
+The main change in this release is the move to a multi-page reporting form,
+where you pick the category first, then the subcategory if relevant, any extra
+questions for that category, photos, problem details, and then user details
+last. Research shows people find a form easier to fill in this way, and it
+makes it clearer what is expected at each step of the process. We have also
+switched from a category drop-down to radio buttons, as this is easier to use,
+especially on mobile.
+
+<p align="center"><img src="/assets/posts/v4-category.jpg"></p>
+
+### Photo redaction
+
+We have added photo redaction support, letting you moderate parts of a photo
+that should not be public without removing the whole photo, and photos can also
+be moderated individually.
+
+<p align="center"><img src="/assets/posts/v4-redaction.gif" width="50%"></p>
+
+### Development Docker environment
+
+We now include a development Docker environment, which should hopefully make it
+easier for people to spin up a local copy of the code for development. If you
+have Docker and Docker Compose installed, a fresh clone and then
+`docker/compose-dev up` should set everything up for you.
+
+### Other improvements
+
+You can now specify a radius when signing up for an email alert, the mobile
+site has an improved navigation menu, users can set global notification
+preferences, and the search box supports Maidenhead Locator references.
+
+A few admin pages have had their layout improved, and you can now customise
+hints on a per-category basis. The CSV export includes device type, staff
+can find non-public reports when using the front page ID search, and user login
+attempts can be throttled per user.
+
+The alert script has been split up, so you can e.g. choose to send local alerts
+at a different frequency to update alerts.
+
+### Bugfixes
+
+As always, we have fixed a number of issues that have arisen – for example, if
+a category has more than 10 extra questions, they should now be sorted in the
+correct order, there was a bug in update text moderation, and categories with
+slashes in no longer break the CSV export.
+
+### Upgrading
+
+A full list of changes can be seen in the
+[v4.0 changelog](https://github.com/mysociety/fixmystreet/releases/tag/v4.0)
+or
+[v3.1.1 changelog](https://github.com/mysociety/fixmystreet/releases/tag/v3.1.1)
+as usual.
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