diff --git a/build_tools/list_committers_since.fish b/build_tools/list_committers_since.fish
new file mode 100755
index 000000000..64c9ae3a0
--- /dev/null
+++ b/build_tools/list_committers_since.fish
@@ -0,0 +1,34 @@
+#! /usr/bin/env fish
+
+set TAG $argv[1]
+
+if test -z "$TAG"
+    echo "Tag name required."
+    exit 1
+end
+
+if not contains -- $TAG (git tag)
+    echo "$TAG is not a valid tag name."
+    exit 1
+end
+
+set committers_to_tag (mktemp)
+set committers_from_tag (mktemp)
+
+# You might think it would be better to case-insensitively sort/compare the names
+# to produce a more natural-looking list.
+# Unicode collation tables mean that this is fraught with danger; for example, the
+# "“" character will not case-fold in UTF-8 locales. sort suggests using the C locale!
+
+git log "$TAG"   --format="%aN" --reverse | sort | uniq > $committers_to_tag
+git log "$TAG".. --format="%aN" --reverse | sort | uniq > $committers_from_tag
+
+echo New committers:
+echo (comm -13 $committers_to_tag $committers_from_tag)','
+
+echo
+
+echo Returning committers:
+echo (comm -12 $committers_to_tag $committers_from_tag)','
+
+rm $committers_to_tag $committers_from_tag