Guided by the question of why and how the Mediterranean Sea, the bond between Europe and its African empires, became a frontier, this chapter explores the formation of two separate migration regimes in Europe. One that is liberal for white migration of the European Communities; the other that is (unevenly) closed and concerns racialized migration of the post-imperial communities. Analysing a period from the 1940s to the late 1970s, this chapter uses archival material from national and European bureaucracies to establish the formation of differentiated mobility and social security regimes by means of international and EEC/EC law. The chapter shows how this process has happened gradually. European law initially recognized the coexistence of two ‘communities’ (one European, one postcolonial), within which the rules of free movement of workers and access to social rights for foreigners from postcolonial and European communities were (formally) equal. Later, national and European bureaucracies gradually established a double standard along racial lines, which became the norm in the 1970s. In so doing, European law has contributed to closing access to the wealth accumulated in the former colonial mainland countries to the racialized populations of the former colonies.