A permanent feature of studies on regional integration is the difficulty of defining the dependent variable (integration) and the application –often simultaneously– of analytical tools from various approaches and theories of social sciences to attempt to overcome this problem. In this paper I will discuss the issue from an International Relations perspective, focusing on the major debates surrounding regional integration, highlighting their particularities and typologies. In the first part I will examine the connection between regionalism and integration and subsequently I will explore the main theories linked to the issue in order to make generalizations. Finally, and based on neofunctionalist approaches I will present a definition of regional integration that revitalizes the notion of transfer loyalties, a key idea that permits the distinction of this concept from other similar ones.