We examine the social network structure of Congress from 1973 to 2004. We treat two Members of Congress as directly linked if they have cosponsored at least one bill together. We then construct explicit networks for each year using data from all forms of legislation, including resolutions, public and private bills, and amendments. We show that Congress exemplifies the characteristics of a ''small world'' network and that the varying small-world properties during this time period are related to the number of important bills passed.