“Winnowing” is the pre-floor process by which Congress determines the small percentage of bills that will receive committee attention. The vast majority of proposals languish in this vital agenda-setting stage, yet our understanding of winnowing is nascent. Why do some bills move forward while most fail? I examine that question here by developing and testing a theoretical framework of winnowing grounded in bounded rationality, which includes institutional and sponsor cues and also incorporates the unique issue milieu. A heteroskedastic probit model is utilized to analyze the winnowing fate of all bills introduced across five issue areas in the House and Senate from 1991 to 1998. The findings counter much received wisdom and suggest that the process is indeed cue based. The majority party helps structure this critical process in both chambers, though party effects appear stronger in the House. Contrary to recent work on the rise of Senate individualism, the seniority of the sponsor has significant effects in both the Senate and House, but again exhibits a stronger effect in the House. Surprisingly, presidential proposals are no more likely to survive than typical bills. The findings further suggest that the entrepreneurial efforts of bill sponsors breathe life into this process.