diff --git a/README.md b/README.md
index ea855e28..cacf77d5 100644
--- a/README.md
+++ b/README.md
@@ -99,3 +99,9 @@ To lint, install requirements (included in the previous step) and run
 ```bash
 make lint
 ```
+
+## Acknowledgmnts
+
+We would like to thank the following people for their contributions:
+
+- [@aadamson](https://github.com/aadamson) for their contributions in supporting custom `requests.Session` objects [#170](https://github.com/sigopt/sigopt-python/pull/170)
diff --git a/requirements-dev.txt b/requirements-dev.txt
index 14c6464e..f37a8f83 100644
--- a/requirements-dev.txt
+++ b/requirements-dev.txt
@@ -1,4 +1,4 @@
 # For continuous integration and development
-mock==1.0.1
+mock>=3.0.5
 pytest==2.8.7
 twine==1.9.1
diff --git a/sigopt/interface.py b/sigopt/interface.py
index 23fc5bee..33dd9edb 100644
--- a/sigopt/interface.py
+++ b/sigopt/interface.py
@@ -274,7 +274,7 @@ class Connection(object):
   Client-facing interface for creating Connections.
   Shouldn't be changed without a major version change.
   """
-  def __init__(self, client_token=None, user_agent=None):
+  def __init__(self, client_token=None, user_agent=None, session=None):
     client_token = client_token or os.environ.get('SIGOPT_API_TOKEN')
     api_url = os.environ.get('SIGOPT_API_URL') or DEFAULT_API_URL
     if not client_token:
@@ -289,6 +289,7 @@ def __init__(self, client_token=None, user_agent=None):
       client_token,
       '',
       default_headers,
+      session=session,
     )
     self.impl = ConnectionImpl(requestor, api_url=api_url)
 
diff --git a/sigopt/requestor.py b/sigopt/requestor.py
index 94fc0c68..70c24f22 100644
--- a/sigopt/requestor.py
+++ b/sigopt/requestor.py
@@ -12,10 +12,11 @@ def __init__(
     user,
     password,
     headers,
-    verify_ssl_certs=True,
+    verify_ssl_certs=None,
     proxies=None,
     timeout=DEFAULT_HTTP_TIMEOUT,
     client_ssl_certs=None,
+    session=None,
   ):
     self._set_auth(user, password)
     self.default_headers = headers or {}
@@ -23,6 +24,7 @@ def __init__(
     self.proxies = proxies
     self.timeout = timeout
     self.client_ssl_certs = client_ssl_certs
+    self.session = session
 
   def _set_auth(self, username, password):
     if username is not None:
@@ -48,7 +50,8 @@ def delete(self, url, params=None, json=None, headers=None):
   def request(self, method, url, params=None, json=None, headers=None):
     headers = self._with_default_headers(headers)
     try:
-      response = requests.request(
+      caller = (self.session or requests)
+      response = caller.request(
         method=method,
         url=url,
         params=params,
diff --git a/test/test_interface.py b/test/test_interface.py
index 3775b513..9ee82d20 100644
--- a/test/test_interface.py
+++ b/test/test_interface.py
@@ -10,12 +10,26 @@ class TestInterface(object):
   def test_create(self):
     conn = Connection(client_token='client_token')
     assert conn.impl.api_url == 'https://api.sigopt.com'
-    assert conn.impl.requestor.verify_ssl_certs is True
+    assert conn.impl.requestor.verify_ssl_certs is None
+    assert conn.impl.requestor.session is None
     assert conn.impl.requestor.proxies is None
     assert conn.impl.requestor.timeout == DEFAULT_HTTP_TIMEOUT
     assert isinstance(conn.clients, ApiResource)
     assert isinstance(conn.experiments, ApiResource)
 
+  def test_create_uses_session_if_provided(self):
+    session = mock.Mock()
+    conn = Connection(client_token='client_token', session=session)
+    assert conn.impl.requestor.session is session
+
+    response = mock.Mock()
+    session.request.return_value = response
+    response.status_code = 200
+    response.text = '{}'
+    session.request.assert_not_called()
+    conn.experiments().fetch()
+    session.request.assert_called_once()
+
   def test_environment_variable(self):
     with mock.patch.dict(os.environ, {'SIGOPT_API_TOKEN': 'client_token'}):
       Connection()