diff --git a/mercurial/hg.py b/mercurial/hg.py
--- a/mercurial/hg.py
+++ b/mercurial/hg.py
@@ -10,7 +10,7 @@ from repo import *
 from demandload import *
 from i18n import gettext as _
 demandload(globals(), "localrepo bundlerepo httprepo sshrepo statichttprepo")
-demandload(globals(), "os util")
+demandload(globals(), "errno lock os shutil util")
 
 def bundle(ui, path):
     if path.startswith('bundle://'):
@@ -73,3 +73,133 @@ def repository(ui, path=None, create=0):
             raise util.Abort(_('cannot create new repository over "%s" protocol') %
                              scheme)
     return ctor(ui, path)
+
+def clone(ui, source, dest=None, pull=False, rev=None, update=True):
+    """Make a copy of an existing repository.
+
+    Create a copy of an existing repository in a new directory.  The
+    source and destination are URLs, as passed to the repository
+    function.  Returns a pair of repository objects, the source and
+    newly created destination.
+
+    The location of the source is added to the new repository's
+    .hg/hgrc file, as the default to be used for future pulls and
+    pushes.
+
+    If an exception is raised, the partly cloned/updated destination
+    repository will be deleted.
+    
+    Keyword arguments:
+
+    dest: URL of destination repository to create (defaults to base
+    name of source repository)
+
+    pull: always pull from source repository, even in local case
+
+    rev: revision to clone up to (implies pull=True)
+
+    update: update working directory after clone completes, if
+    destination is local repository
+    """
+    if dest is None:
+        dest = os.path.basename(os.path.normpath(source))
+
+    if os.path.exists(dest):
+        raise util.Abort(_("destination '%s' already exists"), dest)
+
+    class DirCleanup(object):
+        def __init__(self, dir_):
+            self.rmtree = shutil.rmtree
+            self.dir_ = dir_
+        def close(self):
+            self.dir_ = None
+        def __del__(self):
+            if self.dir_:
+                self.rmtree(self.dir_, True)
+
+    src_repo = repository(ui, source)
+
+    dest_repo = None
+    try:
+        dest_repo = repository(ui, dest)
+        raise util.Abort(_("destination '%s' already exists." % dest))
+    except RepoError:
+        dest_repo = repository(ui, dest, create=True)
+
+    dest_path = None
+    dir_cleanup = None
+    if dest_repo.local():
+        dest_path = os.path.realpath(dest)
+        dir_cleanup = DirCleanup(dest_path)
+
+    abspath = source
+    copy = False
+    if src_repo.local() and dest_repo.local():
+        abspath = os.path.abspath(source)
+        copy = not pull and not rev
+
+    src_lock, dest_lock = None, None
+    if copy:
+        try:
+            # we use a lock here because if we race with commit, we
+            # can end up with extra data in the cloned revlogs that's
+            # not pointed to by changesets, thus causing verify to
+            # fail
+            src_lock = src_repo.lock()
+        except lock.LockException:
+            copy = False
+
+    if copy:
+        # we lock here to avoid premature writing to the target
+        dest_lock = lock.lock(os.path.join(dest_path, ".hg", "lock"))
+
+	# we need to remove the (empty) data dir in dest so copyfiles
+	# can do its work
+	os.rmdir(os.path.join(dest_path, ".hg", "data"))
+        files = "data 00manifest.d 00manifest.i 00changelog.d 00changelog.i"
+        for f in files.split():
+            src = os.path.join(source, ".hg", f)
+            dst = os.path.join(dest_path, ".hg", f)
+            try:
+                util.copyfiles(src, dst)
+            except OSError, inst:
+                if inst.errno != errno.ENOENT:
+                    raise
+
+	# we need to re-init the repo after manually copying the data
+	# into it
+        dest_repo = repository(ui, dest)
+
+    else:
+        revs = None
+        if rev:
+            if not src_repo.local():
+                raise util.Abort(_("clone by revision not supported yet "
+                                   "for remote repositories"))
+            revs = [src_repo.lookup(r) for r in rev]
+
+        if dest_repo.local():
+            dest_repo.pull(src_repo, heads=revs)
+        elif src_repo.local():
+            src_repo.push(dest_repo, revs=revs)
+        else:
+            raise util.Abort(_("clone from remote to remote not supported"))
+
+    if src_lock:
+        src_lock.release()
+
+    if dest_repo.local():
+        fp = dest_repo.opener("hgrc", "w", text=True)
+        fp.write("[paths]\n")
+        fp.write("default = %s\n" % abspath)
+        fp.close()
+
+        if dest_lock:
+            dest_lock.release()
+
+        if update:
+            dest_repo.update(dest_repo.changelog.tip())
+    if dir_cleanup:
+        dir_cleanup.close()
+
+    return src_repo, dest_repo