This dissertation investigates why some members of Congress (MCs) commit themselves to lawmaking in the pursuit of changing public policy – in other words, why some MCs behave as policy wonks. While the Framers envisioned that Congress would be the policymaking engine of the federal government and that some MCs would become master legislators, today Congress is routinely criticized for dysfunction and gridlock. In this context, the behavior of policy wonks is of normative and practical interest, but there remains relatively little research that focuses squarely on these members. I conceptualize policy wonks as MCs who commit to legislating by adopting intense, specialized, and consistent legislative agendas, and I identify policy wonks with a novel measure of legislative commitment based on these three components and using MCs’ slates of bill sponsorships from 1989 through 2008. Building on previous work on legislative entrepreneurship, I argue that MCs commit to legislating and act as policy wonks based on a strategic calculation that weighs the benefits that flow from this behavior against its costs. I find that legislative commitment is associated with MCs’ institutional positions, the characteristics of their districts, and future career advancement and legislative success. The implications of the research are mixed. While some MCs conform with the Framers’ expectations that they be committed legislators, not all the incentives in Congress are aligned to support MCs acting as policy wonks.