diff --git a/botocore/__init__.py b/botocore/__init__.py
index bbc83ce369..7fa5fc601c 100644
--- a/botocore/__init__.py
+++ b/botocore/__init__.py
@@ -28,6 +28,7 @@ def emit(self, record):
 log = logging.getLogger('botocore')
 log.addHandler(NullHandler())
 
+_INITIALIZERS = []
 
 _first_cap_regex = re.compile('(.)([A-Z][a-z]+)')
 _end_cap_regex = re.compile('([a-z0-9])([A-Z])')
@@ -97,3 +98,42 @@ def xform_name(name, sep='_', _xform_cache=_xform_cache):
         transformed = _end_cap_regex.sub(r'\1' + sep + r'\2', s1).lower()
         _xform_cache[key] = transformed
     return _xform_cache[key]
+
+
+def register_initializer(callback):
+    """Register an initializer function for session creation.
+
+    This initializer function will be invoked whenever a new
+    `botocore.session.Session` is instantiated.
+
+    :type callback: callable
+    :param callback: A callable that accepts a single argument
+        of type `botocore.session.Session`.
+
+    """
+    _INITIALIZERS.append(callback)
+
+
+def unregister_initializer(callback):
+    """Unregister an initializer function.
+
+    :type callback: callable
+    :param callback: A callable that was previously registered
+        with `botocore.register_initializer`.
+
+    :raises ValueError: If a callback is provided that is not currently
+        registered as an initializer.
+
+    """
+    _INITIALIZERS.remove(callback)
+
+
+def invoke_initializers(session):
+    """Invoke all initializers for a session.
+
+    :type session: botocore.session.Session
+    :param session: The session to initialize.
+
+    """
+    for initializer in _INITIALIZERS:
+        initializer(session)
diff --git a/botocore/session.py b/botocore/session.py
index 729c2b0e94..856157ab73 100644
--- a/botocore/session.py
+++ b/botocore/session.py
@@ -30,6 +30,7 @@
     UNSIGNED,
     __version__,
     handlers,
+    invoke_initializers,
     monitoring,
     paginate,
     retryhandler,
@@ -148,6 +149,7 @@ def __init__(
         self.session_var_map = SessionVarDict(self, self.SESSION_VARIABLES)
         if session_vars is not None:
             self.session_var_map.update(session_vars)
+        invoke_initializers(self)
 
     def _register_components(self):
         self._register_credential_provider()
diff --git a/tests/unit/test_session.py b/tests/unit/test_session.py
index 1c90ce9f64..153098ccbd 100644
--- a/tests/unit/test_session.py
+++ b/tests/unit/test_session.py
@@ -23,7 +23,12 @@
 import botocore.exceptions
 import botocore.loaders
 import botocore.session
-from botocore import UNSIGNED, client
+from botocore import (
+    UNSIGNED,
+    client,
+    register_initializer,
+    unregister_initializer,
+)
 from botocore.configprovider import ConfigChainFactory
 from botocore.hooks import HierarchicalEmitter
 from botocore.model import ServiceModel
@@ -993,3 +998,32 @@ def test_new_session_with_none_region(self):
         s3_client = self.session.create_client('s3', region_name=None)
         self.assertIsInstance(s3_client, client.BaseClient)
         self.assertTrue(s3_client.meta.region_name is not None)
+
+
+class TestInitializationHooks(BaseSessionTest):
+    def test_can_register_init_hook(self):
+        call_args = []
+
+        def init_hook(session):
+            call_args.append(session)
+
+        register_initializer(init_hook)
+        self.addCleanup(unregister_initializer, init_hook)
+        session = create_session()
+        self.assertEqual(call_args, [session])
+
+    def test_can_unregister_hook(self):
+        call_args = []
+
+        def init_hook(session):
+            call_args.append(session)
+
+        register_initializer(init_hook)
+        unregister_initializer(init_hook)
+        create_session()
+        self.assertEqual(call_args, [])
+
+    def test_unregister_hook_raises_value_error(self):
+        not_registered = lambda session: None
+        with self.assertRaises(ValueError):
+            self.assertRaises(unregister_initializer(not_registered))