Abstract: Lek mating systems are arenas of intense sexual selection, in which mate choice is unfettered by male-female pair bonds or the requirements of offspring care. Current selective pressures from female choice are widely assumed to dictate the elaborate phenotypes and social systems of lekking males. To investigate the process of female choice and the patterns of male fitness it produces, I’ve collected 20 years of behavioral, morphological, and fitness data from a population of lance-tailed manakins, a cooperatively lekking tropical bird. In this species, breeding alpha males have distinctive morphological and behavioral phenotypes, males team up to perform complicated two-male dances for visiting females, and females search extensively to choose their mates. I’ll discuss what we do and don’t know about the mechanisms of sexual selection in manakins, and what it suggests more broadly for the study of sexual selection.