This analysis of bill sponsorship across a variety of issues and Congresses shows that committee membership is the single most important factor shaping a senator's level of issue attention. Constituency demand is of secondary importance. Ideology, partisanship, and national conditions play little or no role. Consistent with a theoretical cost-benefit framework, the results suggest that senators are motivated by the prospect of electoral and policy rewards from successful legislation rather than from mere position taking. The findings attest to the enduring importance of the committee system in a highly individualistic and increasingly partisan Senate.