> In this paper, we identify the causal effect of fraternity membership on college grades and future income levels by exploiting time variation in the college’s social and residential environment. We use the presence of theme houses and non-Greek social houses and the presence of female students on campus, all of which may affect students’ choices bout whether to join a Greek organization, as instruments or reek membership.These changes allow us to identify shifts in he probability of fraternity membership that are plausibly exogenous and, thereby, to estimate the impact of fraternity membership on an individual’s academic and economic performance. We include controls for student human and social capital endowments to alleviate concerns that the policy changes that generate our instruments may have altered the composition of the student body. An additional advantage of using these instruments is that they are clearly choice variables from the perspective of the college administration.