Recent controversies about the National Security Agency's warrantless wiretapping of international calls have overshadowed equally disturbing allegations that the government has acquired access to a huge database of domestic call traffic data, revealing information about times, dates, and numbers called. Although communication content traditionally has been the primary focus of concern about overreaching government surveillance, law enforcement officials are increasingly interested in using sophisticated computer analysis of noncontent traffic data to "map" networks of associations. Despite the rising importance of digitally mediated association, current Fourth Amendment and statutory schemes provide only weak checks on government. The potential to chill association through overreaching relational surveillance is great. This Article argues that the First Amendment's freedom of association guarantees can and do provide a proper framework for regulating relational surveillance and suggests how these guarantees might apply to particular forms of analysis of traffic data.