The political dimension of EU citizenship is undergoing important developments. This chapter takes a close look at these developments and subjects them to a constitutional analysis. The chapter starts by laying out the conceptual and legal framework of political Union citizenship. It subsequently studies how this framework was created. In this section, it becomes apparent how political Union citizenship was first shaped in a process of constitutionalization and democratization and now steers this process itself. How far this process can or should go is dependent upon both political and constitutional considerations. Some of these considerations are discussed in the final section of the chapter which addresses the current challenges facing political Union citizenship.