The sociology of legislators and legislatures is an interdisciplinary approach which focuses on the social interactions, groups, and institutions involved in the process of parliamentary representation. From this perspective, the institutions of representative democracies are the creations of the people running them. In other words, representatives are both the creations and creators of the institutional settings in which they act. The interactions of legislators both inside and outside legislatures are characterized by three types of social relations: the competition for votes, antagonistic cooperation, and principal–agent relations. This article examines the social relations within parliaments (insider–insider relations) and the relations between parliaments and society (insider–outsider relations). It considers how antagonistic cooperation is learned and reinforced in the process of legislative socialization, and how the social interests and preferences of the population are articulated and mediated in the legislature. It also discusses legislative recruitment and how it paradoxically promotes both equality and social closure.