diff --git a/travelperksdk/__init__.py b/travelperksdk/__init__.py
index f83c2e60..c06a2dc1 100644
--- a/travelperksdk/__init__.py
+++ b/travelperksdk/__init__.py
@@ -1,6 +1,7 @@
 """
 TravelPerk init
 """
+from .apis import TravelperkSDK
 from .exceptions import (
     TravelperkSDKError,
     NotFoundError,
@@ -13,6 +14,7 @@
 
 
 __all__ = [
+    'TravelPerkSDK',
     'TravelperkSDKError',
     'NotFoundError',
     'UnauthorizedClientError',
diff --git a/travelperksdk/travelperksdk.py b/travelperksdk/travelperksdk.py
index e69de29b..a963f90c 100644
--- a/travelperksdk/travelperksdk.py
+++ b/travelperksdk/travelperksdk.py
@@ -0,0 +1,139 @@
+"""
+Travelperk Python SDK
+"""
+import json
+from typing import List, Dict
+import requests
+from future.moves.urllib.parse import urlencode
+
+
+class TravelperkSDK:
+    """
+    Travelperk SDK
+    """
+
+    def __init__(self, client_id: str, client_secret: str,
+                 refresh_token: str, environment: str):
+        """
+        Initialize connection to Travelperk
+        :param client_id: Travelperk client_Id
+        :param client_secret: Travelperk client_secret
+        :param refresh_token: Travelperk refresh_token
+        :param environment: production or sandbox
+        """
+        # Initializing variables
+        self.__client_id = client_id
+        self.__client_secret = client_secret
+        self.refresh_token = refresh_token
+
+        if environment.lower() == 'sandbox':
+            self.__base_url = 'https://api.sandbox-travelperk.com'
+            self.__token_url = 'https://app.sandbox-travelperk.com/accounts/oauth2/token/'
+        elif environment.lower() == 'production':
+            self.__base_url = 'https://api.travelperk.com'
+            self.__token_url = 'https://app.travelperk.com/accounts/oauth2/token/'
+        else:
+            raise ValueError('environment can only be prodcution / sandbox')
+
+        self.__access_token = None
+
+        self.update_access_token()
+        self.update_server_url()
+
+    def update_server_url(self):
+        """
+        Update the server url in all API objects.
+        """
+        base_url = self.__base_url
+
+        self.invoices.set_server_url(base_url)
+
+    def update_access_token(self):
+        """
+        Update the access token and change it in all API objects.
+        """
+        self.__get_access_token()
+        access_token = self.__access_token
+
+        self.invoices.change_access_token(access_token)
+
+    def __get_access_token(self):
+        """Get the access token using a HTTP post.
+
+        Returns:
+            A new access token.
+        """
+
+        api_data = {
+            'grant_type': 'refresh_token',
+            'refresh_token': self.refresh_token,
+            'client_id': self.__client_id,
+            'client_secret': self.__client_secret
+        }
+
+        api_data = urlencode(api_data)
+
+        headers = {
+            'Content-Type': 'application/x-www-form-urlencoded'
+        }
+
+        response = requests.post(url=self.__token_url, data=api_data, headers=headers)
+
+        if response.status_code == 200:
+            auth = json.loads(response.text)
+            self.__access_token = auth['access_token']
+            self.refresh_token = auth['refresh_token']
+
+        elif response.status_code == 400:
+            raise BadRequestError('Something wrong with the request body', response.text)
+
+        elif response.status_code == 401:
+            raise UnauthorizedClientError('Wrong client secret or/and refresh token', response.text)
+
+        elif response.status_code == 404:
+            raise NotFoundError('Client ID doesn\'t exist', response.text)
+
+        elif response.status_code == 500:
+            raise InternalServerError('Internal server error', response.text)
+
+        else:
+            raise TravelperkSDKError('Error: {0}'.format(response.status_code), response.text)
+
+    def _get_request(self, object_type: str, api_url: str) -> List[Dict] or Dict:
+        """Create a HTTP GET request.
+
+        Parameters:
+            api_url (str): Url for the wanted API.
+
+        Returns:
+            A response from the request (dict).
+        """
+
+        api_headers = {
+            'Authorization': 'Bearer {0}'.format(self.__access_token),
+            'Accept': 'application/json'
+        }
+
+        response = requests.get(
+            '{0}{1}'.format(self.__server_url, api_url),
+            headers=api_headers
+        )
+
+        if response.status_code == 200:
+            result = json.loads(response.text)
+            return result[object_type]
+
+        elif response.status_code == 400:
+            raise BadRequestError('Something wrong with the request body', response.text)
+
+        elif response.status_code == 401:
+            raise UnauthorizedClientError('Wrong client secret or/and refresh token', response.text)
+
+        elif response.status_code == 404:
+            raise NotFoundError('Client ID doesn\'t exist', response.text)
+
+        elif response.status_code == 500:
+            raise InternalServerError('Internal server error', response.text)
+
+        else:
+            raise TravelperkSDKError('Error: {0}'.format(response.status_code), response.text)