The digital traces of U.S. members of congress on Twitter enable researchers to observe how these public officials interact with one another in a direct and unobtrusive manner. Using data from Twitter and other sources (e.g., roll-call vote data), this study aims to examine how members of congress connect and communicate with one another on Twitter, why they will connect and communicate with one another in such a way, and what effects such connection and communication among members of congress have on their floor vote behavior. The follower-followee and communication networks of members of congress on Twitter demonstrate a high degree of partisan homogeneity. Members of congress prefer to follow or communicate with other members who are similar to them in terms of partisanship, home state, chamber, and public concern. This condition is known as the homophily effect in social network research. However, the magnitude of the homophily effect is mitigated when the effects of endogenous networking mechanisms (i.e., reciprocity and triadic closure) in such networks are controlled. Follower-followee ties can facilitate political discourse among members of congress on Twitter, whereas both follower-followee and communication ties on Twitter increase the likelihood of vote agreement among members of congress. The theoretical, methodological, and practical implications of the findings are addressed.