"Although many characteristics play a role in the choice of a spouse, sociologists have most often examined endogamy and homogamy with respect to race/ethnicity, religion, and socioeconomic status.... I summarize empirical research by answering four questions: (a) To what extent are groups endogamous and how do groups differ in this respect? (b) How has endogamy changed over time? (c) Which factors are related to endogamy? (d) How do various dimensions of partner choice coincide? [I then] discuss strengths and weaknesses of past research."