In a world in which migration and the mixing of peoples are increasing while at the same time multicultural ideology has given rise to the reassertion of putative primordial differences between peoples, interesting questions are raised about the relationships between political rhetoric and social action, groupness and individuality, and the public and the private. The rate of intermarriage is considered by sociologists the most important statistical test of the strength or weakness of structural divisions within societies. What do social anthropologists have to say about heterogamy and homogamy in situations of movement and flux, and what does this tell us about processes of boundary-definition?