diff --git a/pkgmeta/repository.py b/pkgmeta/repository.py
index dad6445..76d1bbd 100644
--- a/pkgmeta/repository.py
+++ b/pkgmeta/repository.py
@@ -1,6 +1,6 @@
 # -*- coding: utf-8 -*-
 import os
-from collections import Mapping
+from collections import MutableMapping
 
 from pkgmeta.exceptions import ReleaseNotFound
 from pkgmeta.config import RepositoryConfig
@@ -10,14 +10,14 @@
 __all__ = ('Repository',)
 
 
-class Repository(Mapping):
+class Repository(MutableMapping):
     """A repository of Python distribution metadata. The structure is
     organized by package name then by release (version)."""
 
     def __init__(self, config):
         if not isinstance(config, RepositoryConfig):
             raise TypeError("Expected a "
-                            "pkgmeta.config.RepositoryConfig object.")
+                            ", pkgmeta.config.RepositoryConfig object.")
         self.config = config
         self.storage = self.config.storage  # For convenience
 
@@ -37,6 +37,16 @@ def __iter__(self):
     def __len__(self):
         return len(self.storage)
 
+    def __setitem__(self, key, value):
+        if not isinstance(value, ReleaseSet):
+            raise TypeError("Expected a pkgmeta.releases.ReleaseSet, "
+                            "received '%s'" % type(value))
+        self.storage[key] = value
+
+    def __delitem__(self, key):
+        raise Exception("Can't remove items from a read-only repository")
+        
+
     # ############## #
     #   Public API   #
     # ############## #
diff --git a/pkgmeta/tests/test_repository.py b/pkgmeta/tests/test_repository.py
index 6e0fdd0..be40ec5 100644
--- a/pkgmeta/tests/test_repository.py
+++ b/pkgmeta/tests/test_repository.py
@@ -3,7 +3,7 @@
 from pkgmeta.tests import unittest
 from pkgmeta.tests.base import BaseTestCase
 from pkgmeta.tests.mock_metadata import ALL_DISTS, SOLARCAL
-from pkgmeta.tests.utils import populate_repo
+from pkgmeta.tests.utils import make_metadata, populate_repo
 
 
 class RepositoryTestCase(BaseTestCase):
@@ -31,7 +31,8 @@ def make_one(self, location=None):
             location = self.repo_directory
         from pkgmeta.config import RepositoryConfig
         from pkgmeta.storage import FS_STORAGE_TYPE
-        config = RepositoryConfig('', type=FS_STORAGE_TYPE, location=location)
+        config = RepositoryConfig('repo', type=FS_STORAGE_TYPE,
+                                  location=location)
         return self.target_cls(config)
 
     def test_init_without_config(self):
@@ -78,3 +79,44 @@ def test_iteration(self):
     def test_len(self):
         repo = self.make_one()
         self.assertEqual(len(repo), len(ALL_DISTS))
+
+
+class RepositoryMutationTestCase(unittest.TestCase):
+    """Test for the mutation of a repository. Specifically checking for
+    addition and deletion."""
+
+    @property
+    def target_cls(self):
+        from pkgmeta.repository import Repository
+        return Repository
+
+    def make_releaseset(self, common, versions, extras={}):
+        from pkgmeta.metadata import Metadata
+        from pkgmeta.releases import ReleaseSet
+        return ReleaseSet(make_metadata(common, versions, extras, cls=Metadata))
+
+    def make_one(self):
+        from pkgmeta.config import RepositoryConfig
+        from pkgmeta.storage import RUNTIME_STORAGE_TYPE
+        config = RepositoryConfig('repo')
+        return self.target_cls(config)
+
+    def test_setting_releaseset(self):
+        repo = self.make_one()
+        #: Make sure the repo is empty to start
+        self.assertEqual(len(repo), 0)
+        #: Set a releaseset
+        release = self.make_releaseset(*SOLARCAL)
+        repo[release.name] = release
+        self.assertEqual(len(repo), 1)
+        self.assertIn(SOLARCAL[0]['name'], repo)
+
+    def test_setting_with_invalid_type(self):
+        repo = self.make_one()
+        #: Make sure the repo is empty to start
+        self.assertEqual(len(repo), 0)
+        #: Set a releaseset
+        release = self.make_releaseset(*SOLARCAL)
+        repo[release.name] = release
+        self.assertEqual(len(repo), 1)
+        self.assertIn(SOLARCAL[0]['name'], repo)