diff --git a/Documentation/git-rerere.txt b/Documentation/git-rerere.txt
new file mode 100644
index 0000000000..8b6b651237
--- /dev/null
+++ b/Documentation/git-rerere.txt
@@ -0,0 +1,177 @@
+git-rerere(1)
+=============
+
+NAME
+----
+git-rerere - Reuse recorded resolve
+
+SYNOPSIS
+--------
+'git-rerere'
+
+
+DESCRIPTION
+-----------
+
+In a workflow that employs relatively long lived topic branches,
+the developer sometimes needs to resolve the same conflict over
+and over again until the topic branches are done (either merged
+to the "release" branch, or sent out and accepted upstream).
+
+This command helps this process by recording conflicted
+automerge results and corresponding hand-resolve results on the
+initial manual merge, and later by noticing the same automerge
+results and applying the previously recorded hand resolution.
+
+[NOTE]
+You need to create `$GIT_DIR/rr-cache` directory to enable this
+command.
+
+DISCUSSION
+----------
+
+When your topic branch modifies overlapping area that your
+master branch (or upstream) touched since your topic branch
+forked from it, you may want to test it with the latest master,
+even before your topic branch is ready to be pushed upstream:
+
+------------
+              o---*---o topic
+             /
+    o---o---o---*---o---o master
+------------
+
+For such a test, you need to merge master and topic somehow.
+One way to do it is to pull master into the topic branch:
+
+------------
+	$ git checkout topic
+	$ git pull . master
+
+              o---*---o---+ topic
+             /           /
+    o---o---o---*---o---o master
+------------
+
+The commits marked with `*` touch the same area in the same
+file; you need to resolve the conflicts when creating the commit
+marked with `+`.  Then you can test the result to make sure your
+work-in-progress still works with what is in the latest master.
+
+After this test merge, there are two ways to continue your work
+on the topic.  The easiest is to build on top of the test merge
+commit `+`, and when your work in the topic branch is finally
+ready, pull the topic branch into master, and/or ask the
+upstream to pull from you.  By that time, however, the master or
+the upstream might have been advanced since the test merge `+`,
+in which case the final commit graph would look like this:
+
+------------
+	$ git checkout topic
+	$ git pull . master
+	$ ... work on both topic and master branches
+	$ git checkout master
+	$ git pull . topic
+
+              o---*---o---+---o---o topic
+             /           /         \
+    o---o---o---*---o---o---o---o---+ master
+------------
+
+When your topic branch is long-lived, however, your topic branch
+would end up having many such "Merge from master" commits on it,
+which would unnecessarily clutter the development history.
+Readers of the Linux kernel mailing list may remember that Linus
+complained about such too frequent test merges when a subsystem
+maintainer asked to pull from a branch full of "useless merges".
+
+As an alternative, to keep the topic branch clean of test
+merges, you could blow away the test merge, and keep building on
+top of the tip before the test merge:
+
+------------
+	$ git checkout topic
+	$ git pull . master
+	$ git reset --hard HEAD^ ;# rewind the test merge
+	$ ... work on both topic and master branches
+	$ git checkout master
+	$ git pull . topic
+
+              o---*---o-------o---o topic
+             /                     \
+    o---o---o---*---o---o---o---o---+ master
+------------
+
+This would leave only one merge commit when your topic branch is
+finally ready and merged into the master branch.  This merge
+would require you to resolve the conflict, introduced by the
+commits marked with `*`.  However, often this conflict is the
+same conflict you resolved when you created the test merge you
+blew away.  `git-rerere` command helps you to resolve this final
+conflicted merge using the information from your earlier hand
+resolve.
+
+Running `git-rerere` command immediately after a conflicted
+automerge records the conflicted working tree files, with the
+usual conflict markers `<<<<<<<`, `=======`, and `>>>>>>>` in
+them.  Later, after you are done resolving the conflicts,
+running `git-rerere` again records the resolved state of these
+files.  Suppose you did this when you created the test merge of
+master into the topic branch.
+
+Next time, running `git-rerere` after seeing a conflicted
+automerge, if the conflict is the same as the earlier one
+recorded, it is noticed and a three-way merge between the
+earlier conflicted automerge, the earlier manual resolution, and
+the current conflicted automerge is performed by the command.
+If this three-way merge resolves cleanly, the result is written
+out to your working tree file, so you would not have to manually
+resolve it.  Note that `git-rerere` leaves the index file alone,
+so you still need to do the final sanity checks with `git diff`
+(or `git diff -c`) and `git update-index` when you are
+satisfied.
+
+As a convenience measure, `git-merge` automatically invokes
+`git-rerere` when it exits with a failed automerge, which
+records it if it is a new conflict, or reuses the earlier hand
+resolve when it is not.  `git-commit` also invokes `git-rerere`
+when recording a merge result.  What this means is that you do
+not have to do anything special yourself (Note: you still have
+to create `$GIT_DIR/rr-cache` directory to enable this command).
+
+In our example, when you did the test merge, the manual
+resolution is recorded, and it will be reused when you do the
+actual merge later with updated master and topic branch, as long
+as the earlier resolution is still applicable.
+
+The information `git-rerere` records is also used when running
+`git-rebase`.  After blowing away the test merge and continuing
+development on the topic branch:
+
+------------
+              o---*---o-------o---o topic
+             /
+    o---o---o---*---o---o---o---o   master
+
+	$ git rebase master topic
+
+				  o---*---o-------o---o topic
+				 /
+    o---o---o---*---o---o---o---o   master
+------------
+
+you could run `git rebase master topic`, to keep yourself
+up-to-date even before your topic is ready to be sent upstream.
+This would result in falling back to three-way merge, and it
+would conflict the same way the test merge you resolved earlier.
+`git-rerere` is run by `git rebase` to help you resolve this
+conflict.
+
+
+Author
+------
+Written by Junio C Hamano <junkio@cox.net>
+
+GIT
+---
+Part of the gitlink:git[7] suite
diff --git a/Documentation/git.txt b/Documentation/git.txt
index e8ef3efa89..2d0ca9d8ed 100644
--- a/Documentation/git.txt
+++ b/Documentation/git.txt
@@ -313,6 +313,9 @@ gitlink:git-rebase[1]::
 gitlink:git-repack[1]::
 	Pack unpacked objects in a repository.
 
+gitlink:git-rerere[1]::
+	Reuse recorded resolution of conflicted merges.
+
 gitlink:git-reset[1]::
 	Reset current HEAD to the specified state.
 
diff --git a/Makefile b/Makefile
index dfd765115c..5c329346ef 100644
--- a/Makefile
+++ b/Makefile
@@ -116,7 +116,7 @@ SCRIPT_SH = \
 
 SCRIPT_PERL = \
 	git-archimport.perl git-cvsimport.perl git-relink.perl \
-	git-shortlog.perl git-fmt-merge-msg.perl \
+	git-shortlog.perl git-fmt-merge-msg.perl git-rerere.perl \
 	git-svnimport.perl git-mv.perl git-cvsexportcommit.perl
 
 SCRIPT_PYTHON = \
diff --git a/git-am.sh b/git-am.sh
index 731ab1fffa..ee6886f300 100755
--- a/git-am.sh
+++ b/git-am.sh
@@ -88,6 +88,7 @@ fall_back_3way () {
     # saying that we reverted all those changes.
 
     git-merge-resolve $orig_tree -- HEAD $his_tree || {
+	    git-rerere
 	    echo Failed to merge in the changes.
 	    exit 1
     }
diff --git a/git-commit.sh b/git-commit.sh
index 10946ed5f9..9c94083757 100755
--- a/git-commit.sh
+++ b/git-commit.sh
@@ -245,6 +245,7 @@ else
 fi
 ret="$?"
 rm -f "$GIT_DIR/COMMIT_MSG" "$GIT_DIR/COMMIT_EDITMSG"
+git-rerere
 
 if test -x "$GIT_DIR"/hooks/post-commit && test "$ret" = 0
 then
diff --git a/git-merge.sh b/git-merge.sh
index 8c0a92c147..dc17baf6e0 100755
--- a/git-merge.sh
+++ b/git-merge.sh
@@ -309,5 +309,6 @@ Conflicts:
 		sed -e 's/^[^	]*	/	/' |
 		uniq
 	} >>"$GIT_DIR/MERGE_MSG"
+	git rerere
 	die "Automatic merge failed; fix up by hand"
 fi
diff --git a/git-rerere.perl b/git-rerere.perl
new file mode 100755
index 0000000000..df119517fe
--- /dev/null
+++ b/git-rerere.perl
@@ -0,0 +1,223 @@
+#!/usr/bin/perl
+#
+# REuse REcorded REsolve.  This tool records a conflicted automerge
+# result and its hand resolution, and helps to resolve future
+# automerge that results in the same conflict.
+#
+# To enable this feature, create a directory 'rr-cache' under your
+# .git/ directory.
+
+use Digest;
+use File::Path;
+use File::Copy;
+
+my $git_dir = $::ENV{GIT_DIR} || ".git";
+my $rr_dir = "$git_dir/rr-cache";
+my $merge_rr = "$git_dir/rr-cache/MERGE_RR";
+
+my %merge_rr = ();
+
+sub read_rr {
+	if (!-f $merge_rr) {
+		%merge_rr = ();
+		return;
+	}
+	my $in;
+	local $/ = "\0";
+	open $in, "<$merge_rr" or die "$!: $merge_rr";
+	while (<$in>) {
+		chomp;
+		my ($name, $path) = /^([0-9a-f]{40})\t(.*)$/s;
+		$merge_rr{$path} = $name;
+	}
+	close $in;
+}
+
+sub write_rr {
+	my $out;
+	open $out, ">$merge_rr" or die "$!: $merge_rr";
+	for my $path (sort keys %merge_rr) {
+		my $name = $merge_rr{$path};
+		print $out "$name\t$path\0";
+	}
+	close $out;
+}
+
+sub compute_conflict_name {
+	my ($path) = @_;
+	my @side = ();
+	my $in;
+	open $in, "<$path"  or die "$!: $path";
+
+	my $sha1 = Digest->new("SHA-1");
+	my $hunk = 0;
+	while (<$in>) {
+		if (/^<<<<<<< .*/) {
+			$hunk++;
+			@side = ([], undef);
+		}
+		elsif (/^=======$/) {
+			$side[1] = [];
+		}
+		elsif (/^>>>>>>> .*/) {
+			my ($one, $two);
+			$one = join('', @{$side[0]});
+			$two = join('', @{$side[1]});
+			if ($two le $one) {
+				($one, $two) = ($two, $one);
+			}
+			$sha1->add($one);
+			$sha1->add("\0");
+			$sha1->add($two);
+			$sha1->add("\0");
+			@side = ();
+		}
+		elsif (@side == 0) {
+			next;
+		}
+		elsif (defined $side[1]) {
+			push @{$side[1]}, $_;
+		}
+		else {
+			push @{$side[0]}, $_;
+		}
+	}
+	close $in;
+	return ($sha1->hexdigest, $hunk);
+}
+
+sub record_preimage {
+	my ($path, $name) = @_;
+	my @side = ();
+	my ($in, $out);
+	open $in, "<$path"  or die "$!: $path";
+	open $out, ">$name" or die "$!: $name";
+
+	while (<$in>) {
+		if (/^<<<<<<< .*/) {
+			@side = ([], undef);
+		}
+		elsif (/^=======$/) {
+			$side[1] = [];
+		}
+		elsif (/^>>>>>>> .*/) {
+			my ($one, $two);
+			$one = join('', @{$side[0]});
+			$two = join('', @{$side[1]});
+			if ($two le $one) {
+				($one, $two) = ($two, $one);
+			}
+			print $out "<<<<<<<\n";
+			print $out $one;
+			print $out "=======\n";
+			print $out $two;
+			print $out ">>>>>>>\n";
+			@side = ();
+		}
+		elsif (@side == 0) {
+			print $out $_;
+		}
+		elsif (defined $side[1]) {
+			push @{$side[1]}, $_;
+		}
+		else {
+			push @{$side[0]}, $_;
+		}
+	}
+	close $out;
+	close $in;
+}
+
+sub find_conflict {
+	my $in;
+	local $/ = "\0";
+	open $in, '-|', qw(git ls-files -z -u) or die "$!: ls-files";
+	my %path = ();
+	my @path = ();
+	while (<$in>) {
+		chomp;
+		my ($mode, $sha1, $stage, $path) =
+		    /^([0-7]+) ([0-9a-f]{40}) ([123])\t(.*)$/s;
+		$path{$path} |= (1 << $stage);
+	}
+	close $in;
+	while (my ($path, $status) = each %path) {
+		if ($status == 14) { push @path, $path; }
+	}
+	return @path;
+}
+
+sub merge {
+	my ($name, $path) = @_;
+	record_preimage($path, "$rr_dir/$name/thisimage");
+	unless (system('merge', map { "$rr_dir/$name/${_}image" }
+		       qw(this pre post))) {
+		my $in;
+		open $in, "<$rr_dir/$name/thisimage" or
+		    die "$!: $name/thisimage";
+		my $out;
+		open $out, ">$path" or die "$!: $path";
+		while (<$in>) { print $out $_; }
+		close $in;
+		close $out;
+		return 1;
+	}
+	return 0;
+}
+
+-d "$rr_dir" || exit(0);
+
+read_rr();
+my %conflict = map { $_ => 1 } find_conflict();
+
+# MERGE_RR records paths with conflicts immediately after merge
+# failed.  Some of the conflicted paths might have been hand resolved
+# in the working tree since then, but the initial run would catch all
+# and register their preimages.
+
+for my $path (keys %conflict) {
+	# This path has conflict.  If it is not recorded yet,
+	# record the pre-image.
+	if (!exists $merge_rr{$path}) {
+		my ($name, $hunk) = compute_conflict_name($path);
+		next unless ($hunk);
+		$merge_rr{$path} = $name;
+		if (! -d "$rr_dir/$name") {
+			mkpath("$rr_dir/$name", 0, 0777);
+			print STDERR "Recorded preimage for '$path'\n";
+			record_preimage($path, "$rr_dir/$name/preimage");
+		}
+	}
+}
+
+# Now some of the paths that had conflicts earlier might have been
+# hand resolved.  Others may be similar to a conflict already that
+# was resolved before.
+
+for my $path (keys %merge_rr) {
+	my $name = $merge_rr{$path};
+
+	# We could resolve this automatically if we have images.
+	if (-f "$rr_dir/$name/preimage" &&
+	    -f "$rr_dir/$name/postimage") {
+		if (merge($name, $path)) {
+			print STDERR "Resolved '$path' using previous resolution.\n";
+			# Then we do not have to worry about this path
+			# anymore.
+			delete $merge_rr{$path};
+			next;
+		}
+	}
+
+	# Let's see if we have resolved it.
+	(undef, my $hunk) = compute_conflict_name($path);
+	next if ($hunk);
+
+	print STDERR "Recorded resolution for '$path'.\n";
+	copy($path, "$rr_dir/$name/postimage");
+	# And we do not have to worry about this path anymore.
+	delete $merge_rr{$path};
+}
+
+# Write out the rest.
+write_rr();
diff --git a/git-reset.sh b/git-reset.sh
index 6c9e58ad9a..fe53fc8065 100755
--- a/git-reset.sh
+++ b/git-reset.sh
@@ -100,4 +100,4 @@ case "$reset_type" in
 	;;
 esac
 
-rm -f "$GIT_DIR/MERGE_HEAD"
+rm -f "$GIT_DIR/MERGE_HEAD" "$GIT_DIR/rr-cache/MERGE_RR"