diff --git a/framework/exceptions.py b/framework/exceptions.py
new file mode 100644
index 0000000..51c9951
--- /dev/null
+++ b/framework/exceptions.py
@@ -0,0 +1,184 @@
+# Copyright 2017 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style
+# license that can be found in the LICENSE file or at
+# https://developers.google.com/open-source/licenses/bsd
+
+"""Exception classes used throughout monorail.
+"""
+from __future__ import print_function
+from __future__ import division
+from __future__ import absolute_import
+
+
+class ErrorAggregator():
+  """Class for holding errors and raising an exception for many."""
+
+  def __init__(self, exc_type):
+    # type: (type) -> None
+    self.exc_type = exc_type
+    self.error_messages = []
+
+  def __enter__(self):
+    return self
+
+  def __exit__(self, exc_type, exc_value, exc_traceback):
+    # If no exceptions were raised within the context, we check
+    # if any error messages were accumulated that we should raise
+    # an exception for.
+    if exc_type == None:
+      self.RaiseIfErrors()
+    # If there were exceptions raised within the context, we do
+    # nothing to suppress them.
+
+  def AddErrorMessage(self, message, *args, **kwargs):
+    # type: (str, *Any, **Any) -> None
+    """Add a new error message.
+
+    Args:
+      message: An error message, to be formatted using *args and **kwargs.
+      *args: passed in to str.format.
+      **kwargs: passed in to str.format.
+    """
+    self.error_messages.append(message.format(*args, **kwargs))
+
+  def RaiseIfErrors(self):
+    # type: () -> None
+    """If there are errors, raise one exception."""
+    if self.error_messages:
+      raise self.exc_type("\n".join(self.error_messages))
+
+
+class Error(Exception):
+  """Base class for errors from this module."""
+  pass
+
+
+class ActionNotSupported(Error):
+  """The user is trying to do something we do not support."""
+  pass
+
+
+class InputException(Error):
+  """Error in user input processing."""
+  pass
+
+
+class ProjectAlreadyExists(Error):
+  """Tried to create a project that already exists."""
+
+
+class FieldDefAlreadyExists(Error):
+  """Tried to create a custom field that already exists."""
+
+
+class ComponentDefAlreadyExists(Error):
+  """Tried to create a component that already exists."""
+
+
+class NoSuchProjectException(Error):
+  """No project with the specified name exists."""
+  pass
+
+
+class NoSuchTemplateException(Error):
+  """No template with the specified name exists."""
+  pass
+
+
+class NoSuchUserException(Error):
+  """No user with the specified name exists."""
+  pass
+
+
+class NoSuchIssueException(Error):
+  """The requested issue was not found."""
+  pass
+
+
+class NoSuchAttachmentException(Error):
+  """The requested attachment was not found."""
+  pass
+
+
+class NoSuchCommentException(Error):
+  """The requested comment was not found."""
+  pass
+
+
+class NoSuchAmendmentException(Error):
+  """The requested amendment was not found."""
+  pass
+
+
+class NoSuchComponentException(Error):
+  """No component with the specified name exists."""
+  pass
+
+
+class InvalidComponentNameException(Error):
+  """The component name is invalid."""
+  pass
+
+
+class InvalidHotlistException(Error):
+  """The specified hotlist is invalid."""
+  pass
+
+
+class NoSuchFieldDefException(Error):
+  """No field def for specified project exists."""
+  pass
+
+
+class InvalidFieldTypeException(Error):
+  """Expected field type and actual field type do not match."""
+  pass
+
+
+class NoSuchIssueApprovalException(Error):
+  """The requested approval for the issue was not found."""
+  pass
+
+
+class CircularGroupException(Error):
+  """Circular nested group exception."""
+  pass
+
+
+class GroupExistsException(Error):
+  """Group already exists exception."""
+  pass
+
+
+class NoSuchGroupException(Error):
+  """Requested group was not found exception."""
+  pass
+
+
+class InvalidExternalIssueReference(Error):
+  """Improperly formatted external issue reference.
+
+  External issue references must be of the form:
+
+      $tracker_shortname/$tracker_specific_id
+
+  For example, issuetracker.google.com issues:
+
+      b/123456789
+  """
+  pass
+
+
+class PageTokenException(Error):
+  """Incorrect page tokens."""
+  pass
+
+
+class FilterRuleException(Error):
+  """Violates a filter rule that should show error."""
+  pass
+
+
+class OverAttachmentQuota(Error):
+  """Project will exceed quota if the current operation is allowed."""
+  pass