This chapter focuses on the political roles and powers of legislatures. It first describes different types of legislatures on the basis of their functions and relationship with the executive branch, before analysing the roles of legislatures within the political system as a whole, as well as several critical aspects of the internal organizational structures of legislatures. It then examines the relationship between the political power and influence of a legislature and the structure of the broader political and party system. The discussion focuses on legislatures within modern democratic political systems, although many points apply to all legislatures, regardless of regime. The chapter also explains how legislature differs from assembly, parliament, and congress.