diff --git a/.gitignore b/.gitignore
index 1c57d4c958..13311f1d5e 100644
--- a/.gitignore
+++ b/.gitignore
@@ -82,6 +82,7 @@ git-mktag
 git-mktree
 git-name-rev
 git-mv
+git-notes
 git-pack-redundant
 git-pack-objects
 git-pack-refs
diff --git a/Documentation/config.txt b/Documentation/config.txt
index e2b8775dd3..7fbf64d24c 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -422,6 +422,19 @@ relatively high IO latencies.  With this set to 'true', git will do the
 index comparison to the filesystem data in parallel, allowing
 overlapping IO's.
 
+core.notesRef::
+	When showing commit messages, also show notes which are stored in
+	the given ref.  This ref is expected to contain files named
+	after the full SHA-1 of the commit they annotate.
++
+If such a file exists in the given ref, the referenced blob is read, and
+appended to the commit message, separated by a "Notes:" line.  If the
+given ref itself does not exist, it is not an error, but means that no
+notes should be printed.
++
+This setting defaults to "refs/notes/commits", and can be overridden by
+the `GIT_NOTES_REF` environment variable.
+
 alias.*::
 	Command aliases for the linkgit:git[1] command wrapper - e.g.
 	after defining "alias.last = cat-file commit HEAD", the invocation
diff --git a/Documentation/git-notes.txt b/Documentation/git-notes.txt
new file mode 100644
index 0000000000..3d93625f9a
--- /dev/null
+++ b/Documentation/git-notes.txt
@@ -0,0 +1,46 @@
+git-notes(1)
+============
+
+NAME
+----
+git-notes - Add/inspect commit notes
+
+SYNOPSIS
+--------
+[verse]
+'git-notes' (edit | show) [commit]
+
+DESCRIPTION
+-----------
+This command allows you to add notes to commit messages, without
+changing the commit.  To discern these notes from the message stored
+in the commit object, the notes are indented like the message, after
+an unindented line saying "Notes:".
+
+To disable commit notes, you have to set the config variable
+core.notesRef to the empty string.  Alternatively, you can set it
+to a different ref, something like "refs/notes/bugzilla".  This setting
+can be overridden by the environment variable "GIT_NOTES_REF".
+
+
+SUBCOMMANDS
+-----------
+
+edit::
+	Edit the notes for a given commit (defaults to HEAD).
+
+show::
+	Show the notes for a given commit (defaults to HEAD).
+
+
+Author
+------
+Written by Johannes Schindelin <johannes.schindelin@gmx.de>
+
+Documentation
+-------------
+Documentation by Johannes Schindelin
+
+GIT
+---
+Part of the gitlink:git[7] suite
diff --git a/Makefile b/Makefile
index 627d4d09ba..27b9569746 100644
--- a/Makefile
+++ b/Makefile
@@ -265,6 +265,7 @@ SCRIPT_SH += git-merge-octopus.sh
 SCRIPT_SH += git-merge-one-file.sh
 SCRIPT_SH += git-merge-resolve.sh
 SCRIPT_SH += git-mergetool.sh
+SCRIPT_SH += git-notes.sh
 SCRIPT_SH += git-parse-remote.sh
 SCRIPT_SH += git-pull.sh
 SCRIPT_SH += git-quiltimport.sh
@@ -377,6 +378,7 @@ LIB_H += ll-merge.h
 LIB_H += log-tree.h
 LIB_H += mailmap.h
 LIB_H += merge-recursive.h
+LIB_H += notes.h
 LIB_H += object.h
 LIB_H += pack.h
 LIB_H += pack-refs.h
@@ -459,6 +461,7 @@ LIB_OBJS += match-trees.o
 LIB_OBJS += merge-file.o
 LIB_OBJS += merge-recursive.o
 LIB_OBJS += name-hash.o
+LIB_OBJS += notes.o
 LIB_OBJS += object.o
 LIB_OBJS += pack-check.o
 LIB_OBJS += pack-refs.o
diff --git a/cache.h b/cache.h
index 45e713e928..2d889deb26 100644
--- a/cache.h
+++ b/cache.h
@@ -371,6 +371,8 @@ static inline enum object_type object_type(unsigned int mode)
 #define GITATTRIBUTES_FILE ".gitattributes"
 #define INFOATTRIBUTES_FILE "info/attributes"
 #define ATTRIBUTE_MACRO_PREFIX "[attr]"
+#define GIT_NOTES_REF_ENVIRONMENT "GIT_NOTES_REF"
+#define GIT_NOTES_DEFAULT_REF "refs/notes/commits"
 
 extern int is_bare_repository_cfg;
 extern int is_bare_repository(void);
@@ -542,6 +544,7 @@ enum rebase_setup_type {
 
 extern enum branch_track git_branch_track;
 extern enum rebase_setup_type autorebase;
+extern char *notes_ref_name;
 
 #define GIT_REPO_VERSION 0
 extern int repository_format_version;
diff --git a/command-list.txt b/command-list.txt
index 3583a33ee9..2dc2c3320c 100644
--- a/command-list.txt
+++ b/command-list.txt
@@ -73,6 +73,7 @@ git-mktag                               plumbingmanipulators
 git-mktree                              plumbingmanipulators
 git-mv                                  mainporcelain common
 git-name-rev                            plumbinginterrogators
+git-notes                               mainporcelain
 git-pack-objects                        plumbingmanipulators
 git-pack-redundant                      plumbinginterrogators
 git-pack-refs                           ancillarymanipulators
diff --git a/commit.c b/commit.c
index aa3b35b6a8..cf72143f58 100644
--- a/commit.c
+++ b/commit.c
@@ -5,6 +5,7 @@
 #include "utf8.h"
 #include "diff.h"
 #include "revision.h"
+#include "notes.h"
 
 int save_commit_buffer = 1;
 
diff --git a/config.c b/config.c
index 790405a213..e5d5b4bd06 100644
--- a/config.c
+++ b/config.c
@@ -469,6 +469,11 @@ static int git_default_core_config(const char *var, const char *value)
 		return 0;
 	}
 
+	if (!strcmp(var, "core.notesref")) {
+		notes_ref_name = xstrdup(value);
+		return 0;
+	}
+
 	if (!strcmp(var, "core.pager"))
 		return git_config_string(&pager_program, var, value);
 
diff --git a/environment.c b/environment.c
index e278bce0ea..0edae21e74 100644
--- a/environment.c
+++ b/environment.c
@@ -45,6 +45,7 @@ enum rebase_setup_type autorebase = AUTOREBASE_NEVER;
 
 /* Parallel index stat data preload? */
 int core_preload_index = 0;
+char *notes_ref_name;
 
 /* This is set by setup_git_dir_gently() and/or git_default_config() */
 char *git_work_tree_cfg;
diff --git a/git-notes.sh b/git-notes.sh
new file mode 100755
index 0000000000..bfdbaa8527
--- /dev/null
+++ b/git-notes.sh
@@ -0,0 +1,65 @@
+#!/bin/sh
+
+USAGE="(edit | show) [commit]"
+. git-sh-setup
+
+test -n "$3" && usage
+
+test -z "$1" && usage
+ACTION="$1"; shift
+
+test -z "$GIT_NOTES_REF" && GIT_NOTES_REF="$(git config core.notesref)"
+test -z "$GIT_NOTES_REF" && GIT_NOTES_REF="refs/notes/commits"
+
+COMMIT=$(git rev-parse --verify --default HEAD "$@") ||
+die "Invalid commit: $@"
+
+MESSAGE="$GIT_DIR"/new-notes-$COMMIT
+trap '
+	test -f "$MESSAGE" && rm "$MESSAGE"
+' 0
+
+case "$ACTION" in
+edit)
+	GIT_NOTES_REF= git log -1 $COMMIT | sed "s/^/#/" > "$MESSAGE"
+
+	GIT_INDEX_FILE="$MESSAGE".idx
+	export GIT_INDEX_FILE
+
+	CURRENT_HEAD=$(git show-ref "$GIT_NOTES_REF" | cut -f 1 -d ' ')
+	if [ -z "$CURRENT_HEAD" ]; then
+		PARENT=
+	else
+		PARENT="-p $CURRENT_HEAD"
+		git read-tree "$GIT_NOTES_REF" || die "Could not read index"
+		git cat-file blob :$COMMIT >> "$MESSAGE" 2> /dev/null
+	fi
+
+	${VISUAL:-${EDITOR:-vi}} "$MESSAGE"
+
+	grep -v ^# < "$MESSAGE" | git stripspace > "$MESSAGE".processed
+	mv "$MESSAGE".processed "$MESSAGE"
+	if [ -s "$MESSAGE" ]; then
+		BLOB=$(git hash-object -w "$MESSAGE") ||
+			die "Could not write into object database"
+		git update-index --add --cacheinfo 0644 $BLOB $COMMIT ||
+			die "Could not write index"
+	else
+		test -z "$CURRENT_HEAD" &&
+			die "Will not initialise with empty tree"
+		git update-index --force-remove $COMMIT ||
+			die "Could not update index"
+	fi
+
+	TREE=$(git write-tree) || die "Could not write tree"
+	NEW_HEAD=$(echo Annotate $COMMIT | git commit-tree $TREE $PARENT) ||
+		die "Could not annotate"
+	git update-ref -m "Annotate $COMMIT" \
+		"$GIT_NOTES_REF" $NEW_HEAD $CURRENT_HEAD
+;;
+show)
+	git show "$GIT_NOTES_REF":$COMMIT
+;;
+*)
+	usage
+esac
diff --git a/notes.c b/notes.c
new file mode 100644
index 0000000000..bd737842d9
--- /dev/null
+++ b/notes.c
@@ -0,0 +1,160 @@
+#include "cache.h"
+#include "commit.h"
+#include "notes.h"
+#include "refs.h"
+#include "utf8.h"
+#include "strbuf.h"
+#include "tree-walk.h"
+
+struct entry {
+	unsigned char commit_sha1[20];
+	unsigned char notes_sha1[20];
+};
+
+struct hash_map {
+	struct entry *entries;
+	off_t count, size;
+};
+
+static int initialized;
+static struct hash_map hash_map;
+
+static int hash_index(struct hash_map *map, const unsigned char *sha1)
+{
+	int i = ((*(unsigned int *)sha1) % map->size);
+
+	for (;;) {
+		unsigned char *current = map->entries[i].commit_sha1;
+
+		if (!hashcmp(sha1, current))
+			return i;
+
+		if (is_null_sha1(current))
+			return -1 - i;
+
+		if (++i == map->size)
+			i = 0;
+	}
+}
+
+static void add_entry(const unsigned char *commit_sha1,
+		const unsigned char *notes_sha1)
+{
+	int index;
+
+	if (hash_map.count + 1 > hash_map.size >> 1) {
+		int i, old_size = hash_map.size;
+		struct entry *old = hash_map.entries;
+
+		hash_map.size = old_size ? old_size << 1 : 64;
+		hash_map.entries = (struct entry *)
+			xcalloc(sizeof(struct entry), hash_map.size);
+
+		for (i = 0; i < old_size; i++)
+			if (!is_null_sha1(old[i].commit_sha1)) {
+				index = -1 - hash_index(&hash_map,
+						old[i].commit_sha1);
+				memcpy(hash_map.entries + index, old + i,
+					sizeof(struct entry));
+			}
+		free(old);
+	}
+
+	index = hash_index(&hash_map, commit_sha1);
+	if (index < 0) {
+		index = -1 - index;
+		hash_map.count++;
+	}
+
+	hashcpy(hash_map.entries[index].commit_sha1, commit_sha1);
+	hashcpy(hash_map.entries[index].notes_sha1, notes_sha1);
+}
+
+static void initialize_hash_map(const char *notes_ref_name)
+{
+	unsigned char sha1[20], commit_sha1[20];
+	unsigned mode;
+	struct tree_desc desc;
+	struct name_entry entry;
+	void *buf;
+
+	if (!notes_ref_name || read_ref(notes_ref_name, commit_sha1) ||
+	    get_tree_entry(commit_sha1, "", sha1, &mode))
+		return;
+
+	buf = fill_tree_descriptor(&desc, sha1);
+	if (!buf)
+		die("Could not read %s for notes-index", sha1_to_hex(sha1));
+
+	while (tree_entry(&desc, &entry))
+		if (!get_sha1(entry.path, commit_sha1))
+			add_entry(commit_sha1, entry.sha1);
+	free(buf);
+}
+
+static unsigned char *lookup_notes(const unsigned char *commit_sha1)
+{
+	int index;
+
+	if (!hash_map.size)
+		return NULL;
+
+	index = hash_index(&hash_map, commit_sha1);
+	if (index < 0)
+		return NULL;
+	return hash_map.entries[index].notes_sha1;
+}
+
+void get_commit_notes(const struct commit *commit, struct strbuf *sb,
+		const char *output_encoding)
+{
+	static const char *utf8 = "utf-8";
+	unsigned char *sha1;
+	char *msg, *msg_p;
+	unsigned long linelen, msglen;
+	enum object_type type;
+
+	if (!initialized) {
+		const char *env = getenv(GIT_NOTES_REF_ENVIRONMENT);
+		if (env)
+			notes_ref_name = getenv(GIT_NOTES_REF_ENVIRONMENT);
+		else if (!notes_ref_name)
+			notes_ref_name = GIT_NOTES_DEFAULT_REF;
+		initialize_hash_map(notes_ref_name);
+		initialized = 1;
+	}
+
+	sha1 = lookup_notes(commit->object.sha1);
+	if (!sha1)
+		return;
+
+	if (!(msg = read_sha1_file(sha1, &type, &msglen)) || !msglen ||
+			type != OBJ_BLOB)
+		return;
+
+	if (output_encoding && *output_encoding &&
+			strcmp(utf8, output_encoding)) {
+		char *reencoded = reencode_string(msg, output_encoding, utf8);
+		if (reencoded) {
+			free(msg);
+			msg = reencoded;
+			msglen = strlen(msg);
+		}
+	}
+
+	/* we will end the annotation by a newline anyway */
+	if (msglen && msg[msglen - 1] == '\n')
+		msglen--;
+
+	strbuf_addstr(sb, "\nNotes:\n");
+
+	for (msg_p = msg; msg_p < msg + msglen; msg_p += linelen + 1) {
+		linelen = strchrnul(msg_p, '\n') - msg_p;
+
+		strbuf_addstr(sb, "    ");
+		strbuf_add(sb, msg_p, linelen);
+		strbuf_addch(sb, '\n');
+	}
+
+	free(msg);
+}
diff --git a/notes.h b/notes.h
new file mode 100644
index 0000000000..79d21b65f5
--- /dev/null
+++ b/notes.h
@@ -0,0 +1,7 @@
+#ifndef NOTES_H
+#define NOTES_H
+
+void get_commit_notes(const struct commit *commit, struct strbuf *sb,
+		const char *output_encoding);
+
+#endif
diff --git a/pretty.c b/pretty.c
index cc460b5697..8d4dbc9fbb 100644
--- a/pretty.c
+++ b/pretty.c
@@ -6,6 +6,7 @@
 #include "string-list.h"
 #include "mailmap.h"
 #include "log-tree.h"
+#include "notes.h"
 #include "color.h"
 
 static char *user_format;
@@ -920,5 +921,9 @@ void pretty_print_commit(enum cmit_fmt fmt, const struct commit *commit,
 	 */
 	if (fmt == CMIT_FMT_EMAIL && sb->len <= beginning_of_body)
 		strbuf_addch(sb, '\n');
+
+	if (fmt != CMIT_FMT_ONELINE)
+		get_commit_notes(commit, sb, encoding);
+
 	free(reencoded);
 }
diff --git a/t/t3301-notes.sh b/t/t3301-notes.sh
new file mode 100755
index 0000000000..9393a25511
--- /dev/null
+++ b/t/t3301-notes.sh
@@ -0,0 +1,95 @@
+#!/bin/sh
+#
+# Copyright (c) 2007 Johannes E. Schindelin
+#
+
+test_description='Test commit notes'
+
+. ./test-lib.sh
+
+cat > fake_editor.sh << \EOF
+echo "$MSG" > "$1"
+echo "$MSG" >& 2
+EOF
+chmod a+x fake_editor.sh
+VISUAL=./fake_editor.sh
+export VISUAL
+
+test_expect_success 'cannot annotate non-existing HEAD' '
+	! MSG=3 git notes edit
+'
+
+test_expect_success setup '
+	: > a1 &&
+	git add a1 &&
+	test_tick &&
+	git commit -m 1st &&
+	: > a2 &&
+	git add a2 &&
+	test_tick &&
+	git commit -m 2nd
+'
+
+test_expect_success 'need valid notes ref' '
+	! MSG=1 GIT_NOTES_REF='/' git notes edit &&
+	! MSG=2 GIT_NOTES_REF='/' git notes show
+'
+
+test_expect_success 'create notes' '
+	git config core.notesRef refs/notes/commits &&
+	MSG=b1 git notes edit &&
+	test ! -f .git/new-notes &&
+	test 1 = $(git ls-tree refs/notes/commits | wc -l) &&
+	test b1 = $(git notes show) &&
+	git show HEAD^ &&
+	! git notes show HEAD^
+'
+
+cat > expect << EOF
+commit 268048bfb8a1fb38e703baceb8ab235421bf80c5
+Author: A U Thor <author@example.com>
+Date:   Thu Apr 7 15:14:13 2005 -0700
+
+    2nd
+
+Notes:
+    b1
+EOF
+
+test_expect_success 'show notes' '
+	! (git cat-file commit HEAD | grep b1) &&
+	git log -1 > output &&
+	test_cmp expect output
+'
+test_expect_success 'create multi-line notes (setup)' '
+	: > a3 &&
+	git add a3 &&
+	test_tick &&
+	git commit -m 3rd &&
+	MSG="b3
+c3c3c3c3
+d3d3d3" git notes edit
+'
+
+cat > expect-multiline << EOF
+commit 1584215f1d29c65e99c6c6848626553fdd07fd75
+Author: A U Thor <author@example.com>
+Date:   Thu Apr 7 15:15:13 2005 -0700
+
+    3rd
+
+Notes:
+    b3
+    c3c3c3c3
+    d3d3d3
+EOF
+
+printf "\n" >> expect-multiline
+cat expect >> expect-multiline
+
+test_expect_success 'show multi-line notes' '
+	git log -2 > output &&
+	test_cmp expect-multiline output
+'
+
+test_done
diff --git a/t/t3302-notes-index-expensive.sh b/t/t3302-notes-index-expensive.sh
new file mode 100755
index 0000000000..00d27bf6ef
--- /dev/null
+++ b/t/t3302-notes-index-expensive.sh
@@ -0,0 +1,98 @@
+#!/bin/sh
+#
+# Copyright (c) 2007 Johannes E. Schindelin
+#
+
+test_description='Test commit notes index (expensive!)'
+
+. ./test-lib.sh
+
+test -z "$GIT_NOTES_TIMING_TESTS" && {
+	say Skipping timing tests
+	test_done
+	exit
+}
+
+create_repo () {
+	number_of_commits=$1
+	nr=0
+	parent=
+	test -d .git || {
+	git init &&
+	tree=$(git write-tree) &&
+	while [ $nr -lt $number_of_commits ]; do
+		test_tick &&
+		commit=$(echo $nr | git commit-tree $tree $parent) ||
+			return
+		parent="-p $commit"
+		nr=$(($nr+1))
+	done &&
+	git update-ref refs/heads/master $commit &&
+	{
+		export GIT_INDEX_FILE=.git/temp;
+		git rev-list HEAD | cat -n | sed "s/^[ 	][ 	]*/ /g" |
+		while read nr sha1; do
+			blob=$(echo note $nr | git hash-object -w --stdin) &&
+			echo $sha1 | sed "s/^/0644 $blob 0	/"
+		done | git update-index --index-info &&
+		tree=$(git write-tree) &&
+		test_tick &&
+		commit=$(echo notes | git commit-tree $tree) &&
+		git update-ref refs/notes/commits $commit
+	} &&
+	git config core.notesRef refs/notes/commits
+	}
+}
+
+test_notes () {
+	count=$1 &&
+	git config core.notesRef refs/notes/commits &&
+	git log | grep "^    " > output &&
+	i=1 &&
+	while [ $i -le $count ]; do
+		echo "    $(($count-$i))" &&
+		echo "    note $i" &&
+		i=$(($i+1));
+	done > expect &&
+	git diff expect output
+}
+
+cat > time_notes << \EOF
+	mode=$1
+	i=1
+	while [ $i -lt $2 ]; do
+		case $1 in
+		no-notes)
+			export GIT_NOTES_REF=non-existing
+		;;
+		notes)
+			unset GIT_NOTES_REF
+		;;
+		esac
+		git log >/dev/null
+		i=$(($i+1))
+	done
+EOF
+
+time_notes () {
+	for mode in no-notes notes
+	do
+		echo $mode
+		/usr/bin/time sh ../time_notes $mode $1
+	done
+}
+
+for count in 10 100 1000 10000; do
+
+	mkdir $count
+	(cd $count;
+
+	test_expect_success "setup $count" "create_repo $count"
+
+	test_expect_success 'notes work' "test_notes $count"
+
+	test_expect_success 'notes timing' "time_notes 100"
+	)
+done
+
+test_done