This paper challenges the existing state-of-knowledge about legislative caucuses by arguing that the caucus system reflects and reinforces formal organizing institutions, such as parties and committees, rather than counterbalancing them. We argue that legislators engage in the caucus system in order to maximize the social utility of their relationships. Using a social network framework, we develop and test hypotheses that seek to ascertain the types of legislators that benefit most from the caucus network. We collect data on the complete population of caucuses and their members from the first session of the 110th U.S. House of Representatives and conduct social network and regression analyses to find evidence that the caucus system both supports the hierarchical structure of the formal leadership institutions and offers a meaningful way for all members to establish and maintain relationships with their colleagues.