diff --git a/setup.py b/setup.py
index 94ddd27c..55efaece 100644
--- a/setup.py
+++ b/setup.py
@@ -25,7 +25,7 @@ except ImportError:
 
 kwargs = {}
 
-version = "3.0"
+version = "3.1.dev1"
 
 distutils.core.setup(
     name="tornado",
diff --git a/tornado/__init__.py b/tornado/__init__.py
index ee50cad6..c6dcdd5b 100644
--- a/tornado/__init__.py
+++ b/tornado/__init__.py
@@ -25,5 +25,5 @@ from __future__ import absolute_import, division, print_function, with_statement
 # is zero for an official release, positive for a development branch,
 # or negative for a release candidate or beta (after the base version
 # number has been incremented)
-version = "3.0"
-version_info = (3, 0, 0, 0)
+version = "3.1.dev1"
+version_info = (3, 1, 0, -100)