diff --git a/doc/hg.1.txt b/doc/hg.1.txt
--- a/doc/hg.1.txt
+++ b/doc/hg.1.txt
@@ -328,30 +328,48 @@ FILES
 NAMED REPOSITORIES
 ------------------
 
-    To give symbolic names to a repository, create a section in .hgrc
-    or .hg/hgrc containing assignments of names to paths.
+To give symbolic names to a repository, create a section in .hgrc
+or .hg/hgrc containing assignments of names to paths. Example:
 
-    Example:
-
+-----------------
 [paths]
 hg = http://selenic.com/hg
 tah = http://hg.intevation.org/mercurial-tah/
+-----------------
+
+
+HOOKS
+-----
+
+Mercurial supports a set of 'hook', commands that get automatically
+executed by various actions such as starting or finishing a commit. To
+specify a hook, simply create an hgrc section like the following:
+
+-----------------
+[hooks]
+precommit = echo "this hook gets executed immediately before a commit"
+commit = hg export $NODE | mail -s "new commit $NODE" commit-list
+-----------------
+
 
 NON_TRANSPARENT PROXY SUPPORT
 -----------------------------
 
-    To access a Mercurial repository through a proxy,
-    create a file $HOME/.hgrc in the following format:
+To access a Mercurial repository through a proxy, create a file
+$HOME/.hgrc in the following format:
 
+--------------
 [http_proxy]
 host=myproxy:8080
 user=<username>
 passwd=<password>
 no=<localhost1>,<localhost2>,<localhost3>,...
+--------------
 
-    "user","passwd" fields are used for authenticating proxies,
-    "no" is a comma-separated list of local host names
-    for which proxy must be bypassed.
+"user","passwd" fields are used for authenticating proxies, "no" is a
+comma-separated list of local host names for which proxy must be
+bypassed.
+
 
 BUGS
 ----
diff --git a/mercurial/hg.py b/mercurial/hg.py
--- a/mercurial/hg.py
+++ b/mercurial/hg.py
@@ -371,6 +371,30 @@ class localrepository:
             if pat.search(f): return True
         return False
 
+    def hook(self, name, **args):
+        s = self.ui.config("hooks", name)
+        if s:
+            self.ui.note("running hook %s: %s\n" % (name, s))
+            old = {}
+            for k, v in args.items():
+                k = k.upper()
+                old[k] = os.environ.get(k, None)
+                os.environ[k] = v
+
+            r = os.system(s)
+
+            for k, v in old.items():
+                if v != None:
+                    os.environ[k] = v
+                else:
+                    del os.environ[k]
+
+            if r:
+                self.ui.warn("abort: %s hook failed with status %d!\n" %
+                             (name, r))
+                return False
+        return True
+
     def tags(self):
         '''return a mapping of tag to node'''
         if not self.tagscache:
@@ -548,6 +572,9 @@ class localrepository:
             self.ui.status("nothing changed\n")
             return
 
+        if not self.hook("precommit"):
+            return 1
+
         p1, p2 = self.dirstate.parents()
         c1 = self.changelog.read(p1)
         c2 = self.changelog.read(p2)
@@ -603,6 +630,10 @@ class localrepository:
             text = edittext
 
         n = self.changelog.add(mn, new, text, tr, p1, p2, user, date)
+
+        if not self.hook("commit", node=hex(n)):
+            return 1
+
         tr.close()
 
         self.dirstate.setparents(n)
diff --git a/tests/test-hook b/tests/test-hook
new file mode 100755
--- /dev/null
+++ b/tests/test-hook
@@ -0,0 +1,9 @@
+#!/bin/sh -x
+
+hg init
+echo "[hooks]" > .hg/hgrc
+echo 'precommit = echo precommit hook' >> .hg/hgrc
+echo 'commit = echo commit hook: $NODE' >> .hg/hgrc
+echo a > a
+hg add a
+hg commit -t "test" -u test -d "0 0"
diff --git a/tests/test-hook.out b/tests/test-hook.out
new file mode 100644
--- /dev/null
+++ b/tests/test-hook.out
@@ -0,0 +1,9 @@
++ hg init
++ echo '[hooks]'
++ echo 'precommit = echo precommit hook'
++ echo 'commit = echo commit hook: $NODE'
++ echo a
++ hg add a
++ hg commit -t test -u test -d '0 0'
+precommit hook
+commit hook: acb14030fe0a21b60322c440ad2d20cf7685a376