This research investigates how the characteristics of residential areas in the city affect where crimes occur. Using data for city blocks in Cleveland and San Diego, the analysis tests three major hypotheses relating crime to (1) household composition, (2) features of the residential environment, and (3) the interaction of the social composition and the features of the residential environment. The results support the major hypotheses and show that a substantial portion of the variance in crime depends on the opportunities provided by the social and physical differentiation of the city.