I focus on three district-level demographic variables indicative of contemporary social cleavages, and construct measures of their influences on partisan representation in American state legislatures during the 1999-2000 years. Using these measures, I examine a series of questions concerning the relationship between social cleavages and state legislative outcomes. I find that district racial composition is the most important constituency-based factor influencing partisan representation and voting in legislatures, but that other constituency variables are also important under various circumstances. I also present OLS regression analyses demonstrating the independent effect of the overall representation of social cleavages on levels of legislative polarization. / text