diff --git a/pyproject.toml b/pyproject.toml
index d01205c..b74466f 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -21,6 +21,7 @@ dev = [
     "mypy>=1.17.0",
     "pytest>=8.4.1",
     "pytest-cov>=6.2.1",
+    "pytest-mock>=3.14.1",
     "ruff>=0.12.3",
     "types-requests-oauthlib>=2.0.0.20250516",
 ]
diff --git a/src/pardner/services/__init__.py b/src/pardner/services/__init__.py
index d8a720e..09a3c85 100644
--- a/src/pardner/services/__init__.py
+++ b/src/pardner/services/__init__.py
@@ -1,3 +1,8 @@
 from pardner.services.base import BaseTransferService as BaseTransferService
-from pardner.services.base import InsufficientScopeException as InsufficientScopeException
-from pardner.services.base import UnsupportedVerticalException as UnsupportedVerticalException
+from pardner.services.base import (
+    InsufficientScopeException as InsufficientScopeException,
+)
+from pardner.services.base import (
+    UnsupportedVerticalException as UnsupportedVerticalException,
+)
+from pardner.services.tumblr import TumblrTransferService as TumblrTransferService
diff --git a/src/pardner/services/base.py b/src/pardner/services/base.py
index f39b065..4a3db36 100644
--- a/src/pardner/services/base.py
+++ b/src/pardner/services/base.py
@@ -1,9 +1,9 @@
 from abc import ABC, abstractmethod
-from typing import Iterable
+from typing import Any, Iterable, Optional
 
 from requests_oauthlib import OAuth2Session
 
-from pardner.verticals.base import Vertical
+from pardner.verticals import Vertical
 
 
 class InsufficientScopeException(Exception):
@@ -32,10 +32,12 @@ class BaseTransferService(ABC):
     OAuth 2.0 and data transfers.
     """
 
+    _authorization_url: str
     _client_secret: str
     _oAuth2Session: OAuth2Session
     _service_name: str
     _supported_verticals: set[Vertical] = set()
+    _token_url: str
     _verticals: set[Vertical] = set()
 
     def __init__(
@@ -129,6 +131,37 @@ def add_verticals(
         self.verticals = new_verticals | self.verticals
         return True
 
+    @abstractmethod
+    def fetch_token(
+        self, code: Optional[str] = None, authorization_response: Optional[str] = None
+    ) -> dict[str, Any]:
+        """
+        Once the end-user authorizes the application to access their data, the
+        resource server sends a request to `redirect_uri` with the authorization code as
+        a parameter. Using this authorization code, this method makes a request to the
+        resource server to obtain the access token.
+
+        One of either `code` or `authorization_response` must not be None.
+
+        :param code: the code obtained from parsing the callback URL which the end-user's
+        browser redirected to.
+        :param authorization_response: the URL (with parameters) the end-user's browser
+        redirected to after authorization.
+
+        :returns: the authorization URL and state, respectively.
+        """
+        pass
+
+    @abstractmethod
+    def authorization_url(self) -> tuple[str, str]:
+        """
+        Builds the authorization URL and state. Once the end-user (i.e., resource owner)
+        navigates to the authorization URL they can begin the authorization flow.
+
+        :returns: the authorization URL and state, respectively.
+        """
+        pass
+
     @abstractmethod
     def scope_for_verticals(self, verticals: Iterable[Vertical]) -> set[str]:
         """
diff --git a/src/pardner/services/tumblr.py b/src/pardner/services/tumblr.py
new file mode 100644
index 0000000..8cb48bb
--- /dev/null
+++ b/src/pardner/services/tumblr.py
@@ -0,0 +1,50 @@
+from typing import Any, Iterable, Optional
+
+from pardner.services import BaseTransferService
+from pardner.verticals import Vertical
+
+
+class TumblrTransferService(BaseTransferService):
+    """
+    Class responsible for obtaining end-user authorization to make requests to
+    Tumblr's API.
+    See API documentation: https://www.tumblr.com/docs/en/api/v2
+    """
+
+    _authorization_url = 'https://www.tumblr.com/oauth2/authorize'
+    _token_url = 'https://api.tumblr.com/v2/oauth2/token'
+
+    def __init__(
+        self,
+        client_id: str,
+        client_secret: str,
+        redirect_uri: str,
+        verticals: set[Vertical] = set(),
+    ) -> None:
+        super().__init__(
+            service_name='Tumblr',
+            client_id=client_id,
+            client_secret=client_secret,
+            redirect_uri=redirect_uri,
+            supported_verticals={Vertical.FeedPost},
+            verticals=verticals,
+        )
+
+    def scope_for_verticals(self, verticals: Iterable[Vertical]) -> set[str]:
+        # Tumblr only needs 'base' for read access requests
+        return {'base'}
+
+    def authorization_url(self) -> tuple[str, str]:
+        return self._oAuth2Session.authorization_url(self._authorization_url)
+
+    def fetch_token(
+        self, code: Optional[str] = None, authorization_response: Optional[str] = None
+    ) -> dict[str, Any]:
+        # Requires client_id
+        return self._oAuth2Session.fetch_token(
+            token_url=self._token_url,
+            code=code,
+            authorization_response=authorization_response,
+            include_client_id=True,
+            client_secret=self._client_secret,
+        )
diff --git a/src/pardner/verticals/base.py b/src/pardner/verticals/base.py
index 3d72cd6..101a45f 100644
--- a/src/pardner/verticals/base.py
+++ b/src/pardner/verticals/base.py
@@ -7,4 +7,4 @@ class Vertical(StrEnum):
     Not all verticals are supported by every transfer service.
     """
 
-    pass
+    FeedPost = 'feed_post'
diff --git a/tests/test_transfer_services/test_base.py b/tests/test_transfer_services/test_base.py
index f4e3601..741e579 100644
--- a/tests/test_transfer_services/test_base.py
+++ b/tests/test_transfer_services/test_base.py
@@ -16,13 +16,18 @@ def __init__(self, supported_verticals, verticals):
         self._supported_verticals = set(supported_verticals)
         self._verticals = set(verticals)
 
+    def authorization_url(self):
+        pass
+
+    def fetch_token(self, code=None, authorization_response=None):
+        pass
+
     def scope_for_verticals(self, verticals):
         return sample_scope
 
 
 @pytest.fixture
 def mock_vertical(monkeypatch):
-    Vertical.FAKE_VERTICAL = 'random_vertical'
     Vertical.NEW_VERTICAL = 'new_vertical'
     Vertical.NEW_VERTICAL_EXTRA_SCOPE = 'new_vertical_unsupported'
 
@@ -34,23 +39,19 @@ def blank_transfer_service(monkeypatch):
 
 def test_add_verticals_raises_exception(mock_vertical, blank_transfer_service):
     with pytest.raises(InsufficientScopeException):
-        blank_transfer_service.add_verticals([Vertical.FAKE_VERTICAL])
+        blank_transfer_service.add_verticals([Vertical.FeedPost])
 
 
 def test_set_verticals_raises_exception(mock_vertical, blank_transfer_service):
     with pytest.raises(UnsupportedVerticalException):
-        blank_transfer_service.verticals = [Vertical.FAKE_VERTICAL]
+        blank_transfer_service.verticals = [Vertical.FeedPost]
 
 
 @pytest.fixture
 def transfer_service(mock_vertical):
     mock_transfer_service = FakeTransferService(
-        [
-            Vertical.FAKE_VERTICAL,
-            Vertical.NEW_VERTICAL,
-            Vertical.NEW_VERTICAL_EXTRA_SCOPE,
-        ],
-        [Vertical.FAKE_VERTICAL],
+        [Vertical.FeedPost, Vertical.NEW_VERTICAL, Vertical.NEW_VERTICAL_EXTRA_SCOPE],
+        [Vertical.FeedPost],
     )
     mock_transfer_service.scope = sample_scope
     return mock_transfer_service
@@ -63,7 +64,7 @@ def test_set_supported_verticals(mock_vertical, transfer_service):
 
 def test_add_supported_verticals(mock_vertical, transfer_service):
     assert transfer_service.add_verticals([Vertical.NEW_VERTICAL])
-    assert transfer_service.verticals == {Vertical.FAKE_VERTICAL, Vertical.NEW_VERTICAL}
+    assert transfer_service.verticals == {Vertical.FeedPost, Vertical.NEW_VERTICAL}
 
 
 def test_add_unsupported_vertical_new_scope_required(
@@ -84,6 +85,6 @@ def _mock_scope_for_verticals(verticals):
     assert not transfer_service._oAuth2Session.access_token
     assert transfer_service.scope == {'fake', 'scope', 'new_scope'}
     assert transfer_service.verticals == {
-        Vertical.FAKE_VERTICAL,
+        Vertical.FeedPost,
         Vertical.NEW_VERTICAL_EXTRA_SCOPE,
     }
diff --git a/tests/test_transfer_services/test_tumblr.py b/tests/test_transfer_services/test_tumblr.py
new file mode 100644
index 0000000..cdea3cb
--- /dev/null
+++ b/tests/test_transfer_services/test_tumblr.py
@@ -0,0 +1,51 @@
+from urllib import parse
+
+import pytest
+
+from pardner.services import TumblrTransferService
+from pardner.verticals import Vertical
+
+sample_scope = {'fake', 'scope'}
+
+
+@pytest.fixture
+def mock_tumblr_transfer_service(monkeypatch, verticals=[Vertical.FeedPost]):
+    return TumblrTransferService(
+        'fake_client_id', 'fake_client_secret', 'https://redirect_uri', verticals
+    )
+
+
+@pytest.mark.parametrize(
+    ['verticals', 'expected_scope'], [([], {'base'}), ([Vertical.FeedPost, {'base'}])]
+)
+def test_scope_for_vertical(mock_tumblr_transfer_service, verticals, expected_scope):
+    assert mock_tumblr_transfer_service.scope_for_verticals(verticals) == expected_scope
+
+
+def test_authorization_url(mock_tumblr_transfer_service):
+    auth_url, state = mock_tumblr_transfer_service.authorization_url()
+
+    auth_url_query = parse.urlsplit(auth_url).query
+    auth_url_params = dict(parse.parse_qsl(auth_url_query))
+
+    assert 'client_id' in auth_url_params
+    assert auth_url_params['client_id'] == 'fake_client_id'
+    assert 'redirect_uri' in auth_url_params
+    assert auth_url_params['redirect_uri'] == 'https://redirect_uri'
+    assert 'state' in auth_url_params
+    assert auth_url_params['state'] == state
+
+
+def test_fetch_token_raises_error(mock_tumblr_transfer_service):
+    with pytest.raises(ValueError):
+        mock_tumblr_transfer_service.fetch_token()
+
+
+def test_fetch_token(mocker, mock_tumblr_transfer_service):
+    mock_oauth2session_request = mocker.patch('requests_oauthlib.OAuth2Session.request')
+    mock_client_parse_request_body_response = mocker.patch(
+        'oauthlib.oauth2.rfc6749.clients.WebApplicationClient.parse_request_body_response'
+    )
+    mock_tumblr_transfer_service.fetch_token(code='123code123')
+    mock_oauth2session_request.assert_called_once()
+    mock_client_parse_request_body_response.assert_called_once()
diff --git a/uv.lock b/uv.lock
index c18378c..9ed3cc2 100644
--- a/uv.lock
+++ b/uv.lock
@@ -218,6 +218,7 @@ dev = [
     { name = "mypy" },
     { name = "pytest" },
     { name = "pytest-cov" },
+    { name = "pytest-mock" },
     { name = "ruff" },
     { name = "types-requests-oauthlib" },
 ]
@@ -233,6 +234,7 @@ dev = [
     { name = "mypy", specifier = ">=1.17.0" },
     { name = "pytest", specifier = ">=8.4.1" },
     { name = "pytest-cov", specifier = ">=6.2.1" },
+    { name = "pytest-mock", specifier = ">=3.14.1" },
     { name = "ruff", specifier = ">=0.12.3" },
     { name = "types-requests-oauthlib", specifier = ">=2.0.0.20250516" },
 ]
@@ -294,6 +296,18 @@ wheels = [
     { url = "https://files.pythonhosted.org/packages/bc/16/4ea354101abb1287856baa4af2732be351c7bee728065aed451b678153fd/pytest_cov-6.2.1-py3-none-any.whl", hash = "sha256:f5bc4c23f42f1cdd23c70b1dab1bbaef4fc505ba950d53e0081d0730dd7e86d5", size = 24644, upload-time = "2025-06-12T10:47:45.932Z" },
 ]
 
+[[package]]
+name = "pytest-mock"
+version = "3.14.1"
+source = { registry = "https://pypi.org/simple" }
+dependencies = [
+    { name = "pytest" },
+]
+sdist = { url = "https://files.pythonhosted.org/packages/71/28/67172c96ba684058a4d24ffe144d64783d2a270d0af0d9e792737bddc75c/pytest_mock-3.14.1.tar.gz", hash = "sha256:159e9edac4c451ce77a5cdb9fc5d1100708d2dd4ba3c3df572f14097351af80e", size = 33241, upload-time = "2025-05-26T13:58:45.167Z" }
+wheels = [
+    { url = "https://files.pythonhosted.org/packages/b2/05/77b60e520511c53d1c1ca75f1930c7dd8e971d0c4379b7f4b3f9644685ba/pytest_mock-3.14.1-py3-none-any.whl", hash = "sha256:178aefcd11307d874b4cd3100344e7e2d888d9791a6a1d9bfe90fbc1b74fd1d0", size = 9923, upload-time = "2025-05-26T13:58:43.487Z" },
+]
+
 [[package]]
 name = "requests"
 version = "2.32.4"