diff --git a/openstack_releases/cmds/validate.py b/openstack_releases/cmds/validate.py
index 418edda3b9..d7a6f6bf18 100644
--- a/openstack_releases/cmds/validate.py
+++ b/openstack_releases/cmds/validate.py
@@ -20,6 +20,7 @@ from __future__ import print_function
 
 import argparse
 import atexit
+import glob
 import os
 import os.path
 import re
@@ -76,6 +77,49 @@ def is_a_hash(val):
     return re.search('^[a-f0-9]{40}$', val, re.I) is not None
 
 
+def validate_series_open(deliverable_info,
+                         series_name, filename,
+                         mk_warning, mk_error):
+    "No releases in the new series until the previous one has a branch."
+    if not deliverable_info.get('releases'):
+        return
+    if series_name == '_independent':
+        # These rules don't apply to independent projects.
+        return
+    deliverables_dir = os.path.dirname(
+        os.path.dirname(filename)
+    )
+    deliverable_base = os.path.basename(filename)
+    pattern = os.path.join(
+        deliverables_dir,
+        '*',
+        deliverable_base,
+    )
+    all_deliverable_files = list(sorted(glob.glob(pattern)))
+    idx = all_deliverable_files.index(filename)
+    if idx == 0:
+        # This is the first deliverable file.
+        return
+    previous_deliverable_file = all_deliverable_files[idx - 1]
+    previous_series = os.path.basename(
+        os.path.dirname(previous_deliverable_file)
+    )
+    expected_branch = 'stable/' + previous_series
+    with open(previous_deliverable_file, 'r') as f:
+        previous_deliverable = yaml.load(f.read())
+        if not previous_deliverable:
+            # An empty file results in None, so convert to dict to
+            # make using the value easier.
+            previous_deliverable = {}
+    for branch in previous_deliverable.get('branches', []):
+        if branch['name'] == expected_branch:
+            # Everything is OK
+            return
+    mk_error(
+        'There is no {} branch defined in {}. Is the {} series open?'.format(
+            expected_branch, previous_deliverable_file, series_name))
+
+
 def validate_launchpad(deliverable_info, mk_warning, mk_error):
     "Look for the launchpad project"
     try:
@@ -634,6 +678,13 @@ def main():
                 mk_warning,
                 mk_error,
             )
+            validate_series_open(
+                deliverable_info,
+                series_name,
+                filename,
+                mk_warning,
+                mk_error,
+            )
         validate_branch_prefixes(
             deliverable_info,
             mk_warning,
diff --git a/openstack_releases/tests/test_validate.py b/openstack_releases/tests/test_validate.py
index 8d5d09bc47..ff55e60ebe 100644
--- a/openstack_releases/tests/test_validate.py
+++ b/openstack_releases/tests/test_validate.py
@@ -14,6 +14,7 @@
 
 from __future__ import unicode_literals
 
+import os
 import textwrap
 
 import fixtures
@@ -1344,3 +1345,136 @@ class TestValidateDriverfixesBranches(base.BaseTestCase):
         print(warnings, errors)
         self.assertEqual(0, len(warnings))
         self.assertEqual(1, len(errors))
+
+
+class TestValidateSeriesOpen(base.BaseTestCase):
+
+    def setUp(self):
+        super(TestValidateSeriesOpen, self).setUp()
+        self.tmpdir = self.useFixture(fixtures.TempDir()).path
+
+    def test_series_is_open(self):
+        series_a_dir = self.tmpdir + '/a'
+        series_a_filename = series_a_dir + '/automaton.yaml'
+        series_b_dir = self.tmpdir + '/b'
+        series_b_filename = series_b_dir + '/automaton.yaml'
+        os.makedirs(series_a_dir)
+        os.makedirs(series_b_dir)
+        branch_data = textwrap.dedent('''
+        ---
+        branches:
+          - name: stable/a
+            location: 1.4.0
+        ''')
+        deliverable_data = textwrap.dedent('''
+        ---
+        releases:
+          - version: 1.5.0
+            projects:
+              - repo: openstack/automaton
+                hash: be2885f544637e6ee6139df7dc7bf937925804dd
+        ''')
+        with open(series_a_filename, 'w') as f:
+            f.write(branch_data)
+        with open(series_b_filename, 'w') as f:
+            f.write(deliverable_data)
+        warnings = []
+        errors = []
+        deliverable_info = yaml.safe_load(deliverable_data)
+        validate.validate_series_open(
+            deliverable_info,
+            'a',
+            series_b_filename,
+            warnings.append,
+            errors.append,
+        )
+        print(warnings, errors)
+        self.assertEqual(0, len(warnings))
+        self.assertEqual(0, len(errors))
+
+    def test_no_earlier_series(self):
+        series_b_dir = self.tmpdir + '/b'
+        series_b_filename = series_b_dir + '/automaton.yaml'
+        os.makedirs(series_b_dir)
+        deliverable_data = textwrap.dedent('''
+        ---
+        releases:
+          - version: 1.5.0
+            projects:
+              - repo: openstack/automaton
+                hash: be2885f544637e6ee6139df7dc7bf937925804dd
+        ''')
+        with open(series_b_filename, 'w') as f:
+            f.write(deliverable_data)
+        warnings = []
+        errors = []
+        deliverable_info = yaml.safe_load(deliverable_data)
+        validate.validate_series_open(
+            deliverable_info,
+            'a',
+            series_b_filename,
+            warnings.append,
+            errors.append,
+        )
+        print(warnings, errors)
+        self.assertEqual(0, len(warnings))
+        self.assertEqual(0, len(errors))
+
+    def test_independent(self):
+        deliverable_data = textwrap.dedent('''
+        ---
+        releases:
+          - version: 1.5.0
+            projects:
+              - repo: openstack/automaton
+                hash: be2885f544637e6ee6139df7dc7bf937925804dd
+        ''')
+        warnings = []
+        errors = []
+        deliverable_info = yaml.safe_load(deliverable_data)
+        validate.validate_series_open(
+            deliverable_info,
+            '_independent',
+            'filename',  # not used
+            warnings.append,
+            errors.append,
+        )
+        print(warnings, errors)
+        self.assertEqual(0, len(warnings))
+        self.assertEqual(0, len(errors))
+
+    def test_no_stable_branch(self):
+        series_a_dir = self.tmpdir + '/a'
+        series_a_filename = series_a_dir + '/automaton.yaml'
+        series_b_dir = self.tmpdir + '/b'
+        series_b_filename = series_b_dir + '/automaton.yaml'
+        os.makedirs(series_a_dir)
+        os.makedirs(series_b_dir)
+        branch_data = textwrap.dedent('''
+        ---
+        ''')
+        deliverable_data = textwrap.dedent('''
+        ---
+        releases:
+          - version: 1.5.0
+            projects:
+              - repo: openstack/automaton
+                hash: be2885f544637e6ee6139df7dc7bf937925804dd
+        ''')
+        with open(series_a_filename, 'w') as f:
+            f.write(branch_data)
+        with open(series_b_filename, 'w') as f:
+            f.write(deliverable_data)
+        warnings = []
+        errors = []
+        deliverable_info = yaml.safe_load(deliverable_data)
+        validate.validate_series_open(
+            deliverable_info,
+            'a',
+            series_b_filename,
+            warnings.append,
+            errors.append,
+        )
+        print(warnings, errors)
+        self.assertEqual(0, len(warnings))
+        self.assertEqual(1, len(errors))