Explanations for ethnic voting have focused primarily on voters' use of ethnicity as a heuristic for evaluating parties or candidates, or on the expressive benefits voting for coethnics may provide. This article describes and tests a largely overlooked explanation for ethnic voting resulting from group norms and social pressure. Employing a combination of experimental and observational data from Kenya--as well as observational data from three other African countries--it finds evidence that many voters have no intrinsic preference for coethnic candidates, but that their desire to conform to the norms of their ethnic community drives them to vote along ethnic lines. The results have important implications for our understanding of ethnic voting, as well as the conditions under which survey respondents provide truthful answers about group-related preferences.