diff --git a/plugins/drop/README.md b/plugins/drop/README.md
new file mode 100644
index 0000000..ac8a086
--- /dev/null
+++ b/plugins/drop/README.md
@@ -0,0 +1,12 @@
+## Drop commits from output
+
+To use the plugin, add the command line flag `--plugin drop=<spec>`.
+The flag can be given multiple times to drop more than one commit.
+
+The <spec> value can be either
+
+ - a comma-separated list of hg hashes in the full form (40
+   hexadecimal characters) to drop the corresponding changesets, or
+
+ - a regular expression pattern to drop all changesets with matching
+   descriptions.
diff --git a/plugins/drop/__init__.py b/plugins/drop/__init__.py
new file mode 100644
index 0000000..f004026
--- /dev/null
+++ b/plugins/drop/__init__.py
@@ -0,0 +1,61 @@
+from __future__ import print_function
+
+import sys, re
+
+
+def build_filter(args):
+    if re.match(r'([A-Fa-f0-9]{40}(,|$))+$', args):
+        return RevisionIdFilter(args.split(','))
+    else:
+        return DescriptionFilter(args)
+
+
+def log(fmt, *args):
+    print(fmt % args, file=sys.stderr)
+    sys.stderr.flush()
+
+
+class FilterBase(object):
+    def __init__(self):
+        self.remapped_parents = {}
+
+    def commit_message_filter(self, commit_data):
+        rev = commit_data['revision']
+
+        mapping = self.remapped_parents
+        parent_revs = [rp for p in commit_data['parents']
+                       for rp in mapping.get(p, [p])]
+
+        commit_data['parents'] = parent_revs
+
+        if self.should_drop_commit(commit_data):
+            log('Dropping revision %i.', rev)
+
+            self.remapped_parents[rev] = parent_revs
+
+            # Head commits cannot be dropped because they have no
+            # children, so detach them to a separate branch.
+            commit_data['branch'] = b'dropped-hg-head'
+            commit_data['parents'] = []
+
+    def should_drop_commit(self, commit_data):
+        return False
+
+
+class RevisionIdFilter(FilterBase):
+    def __init__(self, revision_hash_list):
+        super(RevisionIdFilter, self).__init__()
+        self.unwanted_hg_hashes = {h.encode('ascii', 'strict')
+                                   for h in revision_hash_list}
+
+    def should_drop_commit(self, commit_data):
+        return commit_data['hg_hash'] in self.unwanted_hg_hashes
+
+
+class DescriptionFilter(FilterBase):
+    def __init__(self, pattern):
+        super(DescriptionFilter, self).__init__()
+        self.pattern = re.compile(pattern.encode('ascii', 'strict'))
+
+    def should_drop_commit(self, commit_data):
+        return self.pattern.match(commit_data['desc'])
diff --git a/tests/__init__.py b/tests/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/tests/test_drop_plugin.py b/tests/test_drop_plugin.py
new file mode 100644
index 0000000..fcf92bd
--- /dev/null
+++ b/tests/test_drop_plugin.py
@@ -0,0 +1,223 @@
+import sys, os, subprocess
+from tempfile import TemporaryDirectory
+from unittest import TestCase
+from pathlib import Path
+
+
+class CommitDropTest(TestCase):
+    def test_drop_single_commit_by_hash(self):
+        hash1 = self.create_commit('commit 1')
+        self.create_commit('commit 2')
+
+        self.drop(hash1)
+
+        self.assertEqual(['commit 2'], self.git.log())
+
+    def test_drop_commits_by_desc(self):
+        self.create_commit('commit 1 is good')
+        self.create_commit('commit 2 is bad')
+        self.create_commit('commit 3 is good')
+        self.create_commit('commit 4 is bad')
+
+        self.drop('.*bad')
+
+        expected = ['commit 1 is good', 'commit 3 is good']
+        self.assertEqual(expected, self.git.log())
+
+    def test_drop_sequential_commits_in_single_plugin_instance(self):
+        self.create_commit('commit 1')
+        hash2 = self.create_commit('commit 2')
+        hash3 = self.create_commit('commit 3')
+        hash4 = self.create_commit('commit 4')
+        self.create_commit('commit 5')
+
+        self.drop(','.join((hash2, hash3, hash4)))
+
+        expected = ['commit 1', 'commit 5']
+        self.assertEqual(expected, self.git.log())
+
+    def test_drop_sequential_commits_in_multiple_plugin_instances(self):
+        self.create_commit('commit 1')
+        hash2 = self.create_commit('commit 2')
+        hash3 = self.create_commit('commit 3')
+        hash4 = self.create_commit('commit 4')
+        self.create_commit('commit 5')
+
+        self.drop(hash2, hash3, hash4)
+
+        expected = ['commit 1', 'commit 5']
+        self.assertEqual(expected, self.git.log())
+
+    def test_drop_nonsequential_commits(self):
+        self.create_commit('commit 1')
+        hash2 = self.create_commit('commit 2')
+        self.create_commit('commit 3')
+        hash4 = self.create_commit('commit 4')
+
+        self.drop(','.join((hash2, hash4)))
+
+        expected = ['commit 1', 'commit 3']
+        self.assertEqual(expected, self.git.log())
+
+    def test_drop_head(self):
+        self.create_commit('first')
+        self.create_commit('middle')
+        hash_last = self.create_commit('last')
+
+        self.drop(hash_last)
+
+        self.assertEqual(['first', 'middle'], self.git.log())
+
+    def test_drop_merge_commit(self):
+        initial_hash = self.create_commit('initial')
+        self.create_commit('branch A')
+        self.hg.checkout(initial_hash)
+        self.create_commit('branch B')
+        self.hg.merge()
+        merge_hash = self.create_commit('merge to drop')
+        self.create_commit('last')
+
+        self.drop(merge_hash)
+
+        expected_commits = ['initial', 'branch A', 'branch B', 'last']
+        self.assertEqual(expected_commits, self.git.log())
+        self.assertEqual(['branch B', 'branch A'], self.git_parents('last'))
+
+    def test_drop_different_commits_in_multiple_plugin_instances(self):
+        self.create_commit('good commit')
+        bad_hash = self.create_commit('bad commit')
+        self.create_commit('awful commit')
+        self.create_commit('another good commit')
+
+        self.drop('^awful.*', bad_hash)
+
+        expected = ['good commit', 'another good commit']
+        self.assertEqual(expected, self.git.log())
+
+    def test_drop_same_commit_in_multiple_plugin_instances(self):
+        self.create_commit('good commit')
+        bad_hash = self.create_commit('bad commit')
+        self.create_commit('another good commit')
+
+        self.drop('^bad.*', bad_hash)
+
+        expected = ['good commit', 'another good commit']
+        self.assertEqual(expected, self.git.log())
+
+    def setUp(self):
+        self.tempdir = TemporaryDirectory()
+
+        self.hg = HgDriver(Path(self.tempdir.name) / 'hgrepo')
+        self.hg.init()
+
+        self.git = GitDriver(Path(self.tempdir.name) / 'gitrepo')
+        self.git.init()
+
+        self.export = ExportDriver(self.hg.repodir, self.git.repodir)
+
+    def tearDown(self):
+        self.tempdir.cleanup()
+
+    def create_commit(self, message):
+        self.write_file_data('Data for %r.' % message)
+        return self.hg.commit(message)
+
+    def write_file_data(self, data, filename='test_file.txt'):
+        path = self.hg.repodir / filename
+        with path.open('w') as f:
+            print(data, file=f)
+
+    def drop(self, *spec):
+        self.export.run_with_drop(*spec)
+
+    def git_parents(self, message):
+        matches = self.git.grep_log(message)
+        if len(matches) != 1:
+            raise Exception('No unique commit with message %r.' % message)
+        subject, parents = self.git.details(matches[0])
+        return [self.git.details(p)[0] for p in parents]
+
+
+class ExportDriver:
+    def __init__(self, sourcedir, targetdir, *, quiet=True):
+        self.sourcedir = Path(sourcedir)
+        self.targetdir = Path(targetdir)
+        self.quiet = quiet
+        self.python_executable = str(
+            Path.cwd() / os.environ.get('PYTHON', sys.executable))
+        self.script = Path(__file__).parent / '../hg-fast-export.sh'
+
+    def run_with_drop(self, *plugin_args):
+        cmd = [self.script, '-r', str(self.sourcedir)]
+        for arg in plugin_args:
+            cmd.extend(['--plugin', 'drop=' + arg])
+        output = subprocess.DEVNULL if self.quiet else None
+        subprocess.run(cmd, check=True, cwd=str(self.targetdir),
+                       env={'PYTHON': self.python_executable},
+                       stdout=output, stderr=output)
+
+
+class HgDriver:
+    def __init__(self, repodir):
+        self.repodir = Path(repodir)
+
+    def init(self):
+        self.repodir.mkdir()
+        self.run_command('init')
+
+    def commit(self, message):
+        self.run_command('commit', '-A', '-m', message)
+        return self.run_command('id', '--id', '--debug').strip()
+
+    def log(self):
+        output = self.run_command('log', '-T', '{desc}\n')
+        commits = output.strip().splitlines()
+        commits.reverse()
+        return commits
+
+    def checkout(self, rev):
+        self.run_command('checkout', '-r', rev)
+
+    def merge(self):
+        self.run_command('merge', '--tool', ':local')
+
+    def run_command(self, *args):
+        p = subprocess.run(('hg', '-yq') + args,
+                           cwd=str(self.repodir),
+                           check=True,
+                           text=True,
+                           capture_output=True)
+        return p.stdout
+
+
+class GitDriver:
+    def __init__(self, repodir):
+        self.repodir = Path(repodir)
+
+    def init(self):
+        self.repodir.mkdir()
+        self.run_command('init')
+
+    def log(self):
+        output = self.run_command('log', '--format=%s', '--reverse')
+        return output.strip().splitlines()
+
+    def grep_log(self, pattern):
+        output = self.run_command('log', '--format=%H',
+                                  '-F', '--grep', pattern)
+        return output.strip().splitlines()
+
+    def details(self, commit_hash):
+        fmt = '%s%n%P'
+        output = self.run_command('show', '-s', '--format=' + fmt,
+                                  commit_hash)
+        subject, parents = output.splitlines()
+        return subject, parents.split()
+
+    def run_command(self, *args):
+        p = subprocess.run(('git', '--no-pager') + args,
+                           cwd=str(self.repodir),
+                           check=True,
+                           text=True,
+                           capture_output=True)
+        return p.stdout