diff --git a/.codecov.yml b/.codecov.yml
index 8c6498fe76..a837a83378 100644
--- a/.codecov.yml
+++ b/.codecov.yml
@@ -12,5 +12,5 @@ coverage:
 comment:
   layout: "diff, flags"
   branches:
-    - master
+    - main
   after_n_builds: 2
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 19229dd6d3..66c52af4e8 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -79,7 +79,7 @@ message that the code in question is special and care should be taken.
 
 ## Pull Requests
 
-- To keep the `master` branch stable and facilitate code review we prefer to
+- To keep the `main` branch stable and facilitate code review we prefer to
   have all code changes go through a pull request.
 - Include a newsfragment before merging. This is a file in the
   `newsfragments` folder with a description of your change. Try to make it
@@ -133,4 +133,4 @@ message that the code in question is special and care should be taken.
 [Zen of Python]: https://www.python.org/dev/peps/pep-0020/#the-zen-of-python
 [How to Write a Git Commit Message]: https://chris.beams.io/posts/git-commit
 [The Seven Rules]: https://chris.beams.io/posts/git-commit/#seven-rules
-[news-README]: https://github.com/dials/dials/blob/master/newsfragments/README.MD
+[news-README]: https://github.com/dials/dials/blob/main/newsfragments/README.MD
diff --git a/README.md b/README.md
index 93b8eb7096..d94e9b7de8 100644
--- a/README.md
+++ b/README.md
@@ -3,7 +3,7 @@
 ![Code style: black](https://img.shields.io/badge/code%20style-black-000000.svg)
 [![Language grade: Python](https://img.shields.io/lgtm/grade/python/g/dials/dials.svg?logo=lgtm&logoWidth=18)](https://lgtm.com/projects/g/dials/dials/context:python)
 [![Total alerts](https://img.shields.io/lgtm/alerts/g/dials/dials.svg?logo=lgtm&logoWidth=18)](https://lgtm.com/projects/g/dials/dials/alerts/)
-[![Coverage](https://codecov.io/gh/dials/dials/branch/master/graph/badge.svg)](https://codecov.io/gh/dials/dials)
+[![Coverage](https://codecov.io/gh/dials/dials/branch/main/graph/badge.svg)](https://codecov.io/gh/dials/dials)
 [![Gitter](https://badges.gitter.im/dials/community.svg)](https://gitter.im/dials/community?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge)
 
 X-ray crystallography for structural biology has benefited greatly from a number of advances in recent years including high performance pixel array detectors, new beamlines capable of delivering micron and sub-micron focus and new light sources such as XFELs. The DIALS project is a collaborative endeavour to develop new diffraction integration software to meet the data analysis requirements presented by these recent advances. There are three end goals: to develop an extensible framework for the development of algorithms to analyse X-ray diffraction data; the implementation of algorithms within this framework and finally a set of user facing tools using these algorithms to allow integration of data from diffraction experiments on synchrotron and free electron sources.
diff --git a/installer/README.MD b/installer/README.MD
index cad54e9413..27edafc6ed 100644
--- a/installer/README.MD
+++ b/installer/README.MD
@@ -2,7 +2,7 @@ To set up a DIALS development environment you start off with an empty directory.
 
 On Linux and MacOS you can then run
 ```bash
-$ wget https://raw.githubusercontent.com/dials/dials/master/installer/bootstrap.py
+$ wget https://raw.githubusercontent.com/dials/dials/main/installer/bootstrap.py
 $ python bootstrap.py
 ```
 which will install a complete development environment into the directory `conda_base` and
diff --git a/precommitbx/nagger.py b/precommitbx/nagger.py
index fc5df04bda..0ce698e439 100644
--- a/precommitbx/nagger.py
+++ b/precommitbx/nagger.py
@@ -86,7 +86,7 @@ def nag():
   echo this check by setting the environment variable DIALS_WITHOUT_PRECOMMITS
 fi
 echo You can find more information about contributing to DIALS at:
-echo https://github.com/dials/dials/blob/master/CONTRIBUTING.md
+echo https://github.com/dials/dials/blob/main/CONTRIBUTING.md
 echo
 if [ -z "$DIALS_WITHOUT_PRECOMMITS" ]; then
   exit 1