diff --git a/IkiWiki/Plugin/theme.pm b/IkiWiki/Plugin/theme.pm
new file mode 100644
index 000000000..5e6e4b092
--- /dev/null
+++ b/IkiWiki/Plugin/theme.pm
@@ -0,0 +1,37 @@
+#!/usr/bin/perl
+package IkiWiki::Plugin::theme;
+
+use warnings;
+use strict;
+use IkiWiki 3.00;
+
+sub import {
+	hook(type => "getsetup", id => "theme", call => \&getsetup);
+	hook(type => "checkconfig", id => "theme", call => \&checkconfig);
+}
+
+sub getsetup () {
+	return
+		plugin => {
+			safe => 1,
+			rebuild => 0,
+			section => "web",
+		},
+		theme => {
+			type => "string",
+			example => "actiontabs",
+			description => "name of theme to enable",
+			safe => 1,
+			rebuild => 0,
+		},
+}
+
+my $added=0;
+sub checkconfig () {
+	if (! $added && exists $config{theme} && $config{theme} =~ /^\w+$/) {
+		add_underlay("themes/".$config{theme});
+		$added=1;
+	}
+}
+
+1
diff --git a/Makefile.PL b/Makefile.PL
index 4001c841b..29ec9c209 100755
--- a/Makefile.PL
+++ b/Makefile.PL
@@ -78,7 +78,19 @@ underlay_install:
 			install -m 644 $$file $(DESTDIR)$(PREFIX)/share/ikiwiki/directives/ikiwiki/directive; \
 		fi \
 	done
-	
+
+	# Themes have their style.css appended to the normal one.
+	for theme in themes/*; do \
+		install -d $(DESTDIR)$(PREFIX)/share/ikiwiki/$$theme; \
+		for file in $$theme/*; do \
+			if echo "$$file" | grep -q style.css; then \
+				(cat doc/style.css; cat $$file) >> $(DESTDIR)$(PREFIX)/share/ikiwiki/$$theme/style.css; \
+			elif [ -f "$$file" ]; then \
+				install -m 644 $$file $(DESTDIR)$(PREFIX)/share/ikiwiki/$$file; \
+			fi \
+		done; \
+	done
+
 extra_install: underlay_install
 	# Install example sites.
 	for dir in `cd doc/examples; find . -type d ! -regex '.*\.svn.*'`; do \
diff --git a/debian/changelog b/debian/changelog
index 1f350912e..0d49df676 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -22,6 +22,7 @@ ikiwiki (3.20100611) UNRELEASED; urgency=low
   * git: Gix --gettime to properly support utf8 filenames.
   * attachment: Support Windows paths when taking basename of client-supplied
     file name.
+  * theme: New plugin, allows easily theming a site via the underlay.
 
  -- Joey Hess <joeyh@debian.org>  Fri, 11 Jun 2010 13:39:15 -0400
 
diff --git a/doc/plugins/theme.pm b/doc/plugins/theme.pm
new file mode 100644
index 000000000..7149cc163
--- /dev/null
+++ b/doc/plugins/theme.pm
@@ -0,0 +1,11 @@
+[[!template id=plugin name=theme author="[[Joey]]"]]
+[[!tag type/web]]
+
+The theme plugin allows easily applying a theme to your wiki, by
+configuring the `theme` setting in the setup file with the name of a theme
+to use. The themes you can choose from are all subdirectories, typically
+inside `/usr/share/ikiwiki/themes/`.
+
+A theme provides, via the underlay, an enhanced version of the regular
+[[style.css]]. This leaves [[local.css]] free for you to further
+customise. Themes can also provide header and background images.
diff --git a/underlays/themes/actiontabs/style.css b/themes/actiontabs/style.css
similarity index 100%
rename from underlays/themes/actiontabs/style.css
rename to themes/actiontabs/style.css
diff --git a/underlays/themes/bzed/background_darkness.png b/themes/bzed/background_darkness.png
similarity index 100%
rename from underlays/themes/bzed/background_darkness.png
rename to themes/bzed/background_darkness.png
diff --git a/underlays/themes/bzed/style.css b/themes/bzed/style.css
similarity index 100%
rename from underlays/themes/bzed/style.css
rename to themes/bzed/style.css