diff --git a/sparkpost/base.py b/sparkpost/base.py
index 4c3c467..bb721ed 100644
--- a/sparkpost/base.py
+++ b/sparkpost/base.py
@@ -32,10 +32,12 @@ def uri(self):
         return "%s/%s" % (self.base_uri, self.key)
 
     def request(self, method, uri, **kwargs):
+        subaccount = kwargs.pop('subaccount', 0)
         headers = {
             'User-Agent': 'python-sparkpost/' + sparkpost.__version__,
             'Content-Type': 'application/json',
-            'Authorization': self.api_key
+            'Authorization': self.api_key,
+            'X-MSYS-SUBACCOUNT': subaccount
         }
         response = self.transport.request(method, uri, headers=headers,
                                           **kwargs)
diff --git a/sparkpost/transmissions.py b/sparkpost/transmissions.py
index dcb7f86..4729fe2 100644
--- a/sparkpost/transmissions.py
+++ b/sparkpost/transmissions.py
@@ -251,15 +251,18 @@ def send(self, **kwargs):
         """
 
         payload = self._translate_keys(**kwargs)
-        results = self.request('POST', self.uri, data=json.dumps(payload))
+        subaccount = kwargs.pop('subaccount', 0)
+        results = self.request('POST', self.uri, data=json.dumps(payload),
+                               subaccount=subaccount)
         return results
 
-    def _fetch_get(self, transmission_id):
+    def _fetch_get(self, transmission_id, **kwargs):
         uri = "%s/%s" % (self.uri, transmission_id)
-        results = self.request('GET', uri)
+        subaccount = kwargs.pop('subaccount', 0)
+        results = self.request('GET', uri, subaccount=subaccount)
         return results
 
-    def get(self, transmission_id):
+    def get(self, transmission_id, **kwargs):
         """
         Get a transmission by ID
 
@@ -268,7 +271,7 @@ def get(self, transmission_id):
         :returns: the requested transmission if found
         :raises: :exc:`SparkPostAPIException` if transmission is not found
         """
-        results = self._fetch_get(transmission_id)
+        results = self._fetch_get(transmission_id, **kwargs)
         return results['transmission']
 
     def list(self, **kwargs):
@@ -285,9 +288,11 @@ def list(self, **kwargs):
         'check https://sparkpo.st/5qcj4.'
 
         warnings.warn(warn_msg, DeprecationWarning)
-        return self.request('GET', self.uri, params=kwargs)
+        subaccount = kwargs.pop('subaccount', 0)
+        return self.request('GET', self.uri, params=kwargs,
+                            subaccount=subaccount)
 
-    def delete(self, transmission_id):
+    def delete(self, transmission_id, **kwargs):
         """
         Delete a transmission by ID
 
@@ -298,5 +303,6 @@ def delete(self, transmission_id):
             or Canceled
         """
         uri = "%s/%s" % (self.uri, transmission_id)
-        results = self.request('DELETE', uri)
+        subaccount = kwargs.pop('subaccount', 0)
+        results = self.request('DELETE', uri, subaccount=subaccount)
         return results
diff --git a/test/test_base.py b/test/test_base.py
index aff6b79..f02cf09 100644
--- a/test/test_base.py
+++ b/test/test_base.py
@@ -1,7 +1,9 @@
 import pytest
 import responses
+from mock import patch
 
-from sparkpost.base import Resource
+import sparkpost
+from sparkpost.base import Resource, RequestsTransport
 from sparkpost.exceptions import SparkPostAPIException
 
 
@@ -22,6 +24,40 @@ def test_uri():
     assert resource.uri == fake_uri
 
 
+def test_default_headers():
+    expected_headers = {
+        'User-Agent': 'python-sparkpost/' + sparkpost.__version__,
+        'Content-Type': 'application/json',
+        'Authorization': fake_api_key,
+        'X-MSYS-SUBACCOUNT': 0
+    }
+
+    with patch.object(RequestsTransport,
+                      'request',
+                      return_value=None) as request_mock:
+        resource = create_resource()
+        resource.request('GET', resource.uri)
+        request_mock.assert_called_with('GET', resource.uri,
+                                        headers=expected_headers)
+
+
+def test_subaccount_header():
+    expected_headers = {
+        'User-Agent': 'python-sparkpost/' + sparkpost.__version__,
+        'Content-Type': 'application/json',
+        'Authorization': fake_api_key,
+        'X-MSYS-SUBACCOUNT': 123
+    }
+
+    with patch.object(RequestsTransport,
+                      'request',
+                      return_value=None) as request_mock:
+        resource = create_resource()
+        resource.request('GET', resource.uri, subaccount=123)
+        request_mock.assert_called_with('GET', resource.uri,
+                                        headers=expected_headers)
+
+
 @responses.activate
 def test_success_request():
     responses.add(