This chapter examines the history of European Union institutions, and especially the quasi-constant change that has taken place since the creation of the EU. It begins with a discussion of five phases of EU institutional development: the founding, consolidation of the European Community model, institutional change through task extension, reform of the institutional system, and the brief ‘constitutional’ moment at the turn of the century. It then considers the euro crisis and Brexit, along with the respective weight of state interests, ideas, and institutions in the evolution of EU institutions. It shows how institutional change in the EU seems to have followed a functionalist logic, leading to complex compromises that, in turn, prompt regular calls for ‘simplification’ and democratization.