This chapter analyses theories of European integration through a gender lens. It points to the diversity of perspectives in gender scholarship on European integration, and draws on these different points of view to examine other theoretical approaches. It assumes that gender is a basic organising principle of the social world, and therefore is an integral aspect of European integration. The chapter discusses gender theory and its contribution to the study of European integration. It then goes on to interrogate other European integration theories - liberal intergovernmentalism, neofunctionalism, and social constructivism – examining the nature of gendered power that they emphasize and evaluating the extent to which they are open to incorporating a gender-informed perspective. The chapter then analyses the integrationist effect of the European economic crisis on gender equality. This discussion reveals the marginalization of gender equality, and gender mainstreaming, as the neo-liberal response to the economic crisis created new gender inequalities and perpetuated old patterns of gender hierarchy.