diff --git a/CHANGELOG.md b/CHANGELOG.md
index 6910de41..9d3fe9cc 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -16,6 +16,8 @@ how a consumer would use the library (e.g. adding unit tests, updating documenta
 
 - `sdk.legalhold.get_all_events()` to search for legal hold events.
 
+- `sdk.users.update_user()` to update an existing user in Code42.
+
 ### Fixed
 
 - Bug where proxy settings were not being applied correctly.
diff --git a/src/py42/services/users.py b/src/py42/services/users.py
index 398ba2c7..077d382d 100644
--- a/src/py42/services/users.py
+++ b/src/py42/services/users.py
@@ -330,3 +330,43 @@ def remove_role(self, user_id, role_name):
         role_name = quote(role_name)
         uri = u"/api/UserRole?userId={}&roleName={}".format(user_id, role_name)
         return self._connection.delete(uri)
+
+    def update_user(
+        self,
+        user_uid,
+        username=None,
+        email=None,
+        password=None,
+        first_name=None,
+        last_name=None,
+        notes=None,
+        quota=None,
+    ):
+        """Updates an existing user.
+        `REST Documentation <https://console.us.code42.com/apidocviewer/#User-put>`__
+
+        Args:
+            user_uid (int): A Code42 user UID.
+            username (str, optional): The username to which the user's username will be changed. Defaults to None.
+            email (str, optional): The email to which the user's email will be changed. Defaults to None.
+            password (str, optional): The password to which the user's password will be changed. Defaults to None.
+            first_name (str, optional): The first name to which the user's first name will be changed. Defaults to None.
+            last_name (str, optional): The last name to which the user's last name will be changed. Defaults to None.
+            notes (str, optional): Descriptive information about the user. Defaults to None.
+            quota (int, optional): The quota in bytes that limits the user's archive size. Defaults to None.
+
+        Returns:
+            :class:`py42.response.Py42Response`
+        """
+
+        uri = u"/api/User/{}?idType=uid".format(user_uid)
+        data = {
+            u"username": username,
+            u"email": email,
+            u"password": password,
+            u"firstName": first_name,
+            u"lastName": last_name,
+            u"notes": notes,
+            u"quota": quota,
+        }
+        return self._connection.put(uri, json=data)
diff --git a/tests/services/test_users.py b/tests/services/test_users.py
index 38926188..eae2294b 100644
--- a/tests/services/test_users.py
+++ b/tests/services/test_users.py
@@ -52,6 +52,14 @@ def post_api_mock_response(self, mocker):
         response.text = MOCK_text
         return Py42Response(response)
 
+    @pytest.fixture
+    def put_api_mock_response(self, mocker):
+        response = mocker.MagicMock(spec=Response)
+        response.status_code = 200
+        response.encoding = "utf-8"
+        response.text = MOCK_text
+        return Py42Response(response)
+
     @pytest.fixture
     def post_api_mock_error_response(self, mocker):
         response = mocker.MagicMock(spec=Response)
@@ -215,3 +223,58 @@ def side_effect(url, json):
 
         expected = u"Cannot deactivate the user with ID 1234 as the user is involved in a legal hold matter."
         assert str(err.value) == expected
+
+    def test_update_user_calls_put_with_expected_url_and_params(
+        self, mock_connection, put_api_mock_response
+    ):
+        user_service = UserService(mock_connection)
+        mock_connection.post.return_value = put_api_mock_response
+        user_id = "TEST_USER_ID"
+        expected_uri = "{}/{}?idType=uid".format(USER_URI, user_id)
+        username = "TEST_ORG@TEST.COM"
+        email = "TEST_EMAIL@TEST.com"
+        password = "password"
+        first_name = "FIRSTNAME"
+        last_name = "LASTNAME"
+        note = "Test Note"
+        quota = 12345
+        user_service.update_user(
+            user_id,
+            username=username,
+            email=email,
+            password=password,
+            first_name=first_name,
+            last_name=last_name,
+            notes=note,
+            quota=quota,
+        )
+        expected_params = {
+            u"username": username,
+            u"email": email,
+            u"password": password,
+            u"firstName": first_name,
+            u"lastName": last_name,
+            u"notes": note,
+            u"quota": quota,
+        }
+        mock_connection.put.assert_called_once_with(expected_uri, json=expected_params)
+
+    def test_update_user_does_not_include_empty_params(
+        self, mock_connection, put_api_mock_response
+    ):
+        user_service = UserService(mock_connection)
+        mock_connection.post.return_value = put_api_mock_response
+        user_id = "TEST_USER_ID"
+        expected_uri = "{}/{}?idType=uid".format(USER_URI, user_id)
+        username = "TEST_ORG@TEST.COM"
+        user_service.update_user(user_id, username=username)
+        expected_params = {
+            u"username": username,
+            u"email": None,
+            u"password": None,
+            u"firstName": None,
+            u"lastName": None,
+            u"notes": None,
+            u"quota": None,
+        }
+        mock_connection.put.assert_called_once_with(expected_uri, json=expected_params)