Scholars continue to debate the degree to which electoral institutions matter for representation. The literature predicts that minorities benefit from districts while women benefit from at-large elections. The mechanisms by which institutions affect the ability of traditionally underrepresented groups to win seats have been understudied. Using an analysis of over 7,000 cities and interviews with city councilors, we find that compared to at-large systems, district systems can increase diversity only when underrepresented groups are highly concentrated and compose a substantial portion of the population. In addition, we find that the electoral system has a significant effect on representation only for African American male and white female councilors; the proportion of African American women and Latina councilors is not affected by the use of either district or at-large systems.