Paper abstract: Party leaders play a central but dimly understood role in shaping the pool of candidates voters can choose from. Although many political observers blame these gatekeepers for exacerbating polarization by recruiting extremists and for discouraging women and blue-collar workers from running for office, we know little about how party leaders actually evaluate potential candidates for their party’s nomination. In this paper, we shed new light on what these 222 gatekeepers look for in candidates with an original survey of roughly 6,000 leaders of county-level political parties. We find that party leaders prefer candidates with the valence characteristics voters find appealing—e.g., honesty, intelligence, dedication—suggesting that they play an important role in recruiting the kinds of leaders the electorate wants. However, party leaders also use their influence to discourage moderates from seeking office: they strongly prefer candidates at least as ideologically polarized as their median party member. Republican party leaders show this preference especially. Last, party leaders exhibit some biases against blue-collar workers but show little bias against women. These findings have important implications for research on candidate recruitment, party polarization, and the underrepresentation of women and the working class.