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+# Contributing to the tz code and data
+
+Please do not create issues or pull requests on GitHub, as the
+proper procedure for proposing and distributing patches is via
+email as described below.
+
+The time zone database is by no means authoritative: governments
+change timekeeping rules erratically and sometimes with little
+warning, the data entries do not cover all of civil time before
+1970, and undoubtedly errors remain in the code and data.  Feel
+free to fill gaps or fix mistakes, and please email improvements
+to <tz@iana.org> for use in the future.  In your email, please give
+reliable sources that reviewers can check.
+
+## Contributing technical changes
+
+To email small changes, please run a POSIX shell command like
+'diff -u old/europe new/europe >myfix.patch', and attach
+'myfix.patch' to the email.
+
+For more-elaborate or possibly controversial changes,
+such as renaming, adding or removing zones, please read
+"Theory and pragmatics of the tz code and data"
+<https://www.iana.org/time-zones/repository/theory.html>.
+It is also good to browse the mailing list archives
+<https://mm.icann.org/pipermail/tz/> for examples of patches that tend
+to work well.  Additions to data should contain commentary citing
+reliable sources as justification.  Citations should use "https:" URLs
+if available.
+
+For changes that fix sensitive security-related bugs, please see the
+distribution's 'SECURITY' file.
+
+Please submit changes against either the latest release
+<https://www.iana.org/time-zones> or the main branch of the development
+repository.  The latter is preferred.
+
+## Sample Git workflow for developing contributions
+
+If you use Git the following workflow may be helpful:
+
+  * Copy the development repository.
+
+        git clone https://github.com/eggert/tz.git
+        cd tz
+
+  * Get current with the main branch.
+
+        git checkout main
+        git pull
+
+  * Switch to a new branch for the changes.  Choose a different
+    branch name for each change set.
+
+        git checkout -b mybranch
+
+  * Sleuth by using 'git blame'.  For example, when fixing data for
+    Africa/Sao_Tome, if the command 'git blame africa' outputs a line
+    '2951fa3b (Paul Eggert 2018-01-08 09:03:13 -0800 1068) Zone
+    Africa/Sao_Tome 0:26:56 - LMT 1884', commit 2951fa3b should
+    provide some justification for the 'Zone Africa/Sao_Tome' line.
+
+  * Edit source files.  Include commentary that justifies the
+    changes by citing reliable sources.
+
+  * Debug the changes, e.g.:
+
+        make check
+        make install
+        ./zdump -v America/Los_Angeles
+
+  * For each separable change, commit it in the new branch, e.g.:
+
+        git add northamerica
+        git commit
+
+    See recent 'git log' output for the commit-message style.
+
+  * Create patch files 0001-..., 0002-..., ...
+
+        git format-patch main
+
+  * After reviewing the patch files, send the patches to <tz@iana.org>
+    for others to review.
+
+        git send-email main
+
+    For an archived example of such an email, see
+    "[PROPOSED] Fix off-by-1 error for Jamaica and T&C before 1913"
+    <https://mm.icann.org/pipermail/tz/2018-February/026122.html>.
+
+  * Start anew by getting current with the main branch again
+    (the second step above).
+
+-----
+
+This file is in the public domain.