This dissertation builds on existing scholarship in political science and political sociology to explore the influence of interest groups in legislative action networks. The primary theoretical insight is that as the number of interest group affiliations between two members of Congress increases, so does the frequency with which they forge other sorts of social ties necessary to advance the interests of their interest group constituencies. In particular, the analysis looks at interest group donation strategies, legislative co-sponsorships, and roll-call votes during the 111th Congress (2009-2010). The analysis uses social network analysis methods to create network models of 19 different policy domains, as well as an aggregate model, for both the House and Senate. Legislator ideology, state, committee assignments, and experience have a generally significant impact on the number of interest group affiliations shared by each pair of legislators, whereas gender, race/ethnicity, office location and occupational history do not. The results show that interest groups do have consistent impact over co-sponsorships in the House, but somewhat more mixed influence in the Senate. In some instances, groups in the policy domain encourage policy change, and in other instances, status quo protection. The theory did not anticipate the latter effect, though it does make sense in context of other research findings. For roll-call votes, interest groups have a significant influence over some House policy domains but not many Senate policy domains. The increased polarization of the Senate, necessity of minority party discipline to maximize their leverage through use of the filibuster, and staggered nature of Senate elections makes interest group influence tougher to muster in the upper chamber of Congress.