This page links to the various copies of release notes available at mediawiki.org.
Release notes for point releases are included with the main release notes (e.g. release notes for 1.18.1 were added to the release notes for 1.18).
The release notes are maintained as part of every MediaWiki distribution; the release notes for its version are in a
RELEASE-NOTES-1.NN file, and all previous release notes going back to MediaWiki 1.3 are in the
See MediaWiki version lifecycle for target dates of future releases.
The branch points are for internal and public releases. The actual commits that made the branches are tracked:
Release notes for earlier versions of MediaWiki that are not listed above, are available in the distribution package, and also in SVN, though you may need to do a bit of digging.