The publication of Ethnic Groups and Boundaries in 1969 by Fredrik Barth and his colleagues at the University of Bergen launched a remarkably fruitful way of analyzing ethnic group relations and identities. It drew out the arguments of Barth’s teacher Edmund Leach in Political Systems of Highland Burma (1954), concerning identity transformations among Shan and Kachin (though that book was more often cited for its analysis of ritual and of gumsa and gumlao political arrangements). Adopting Leach’s strategizing individual as the center of social processes, 1 Barth and his colleagues developed an entire school for studying ethnicity. Although additional instruments toward this end have emerged since, 2 the Barthian model presented in Ethnic Groups and Boundaries remains an essential ingredient of any analysis of ethnic relations, in anthropology and beyond. It is wholly fitting that we should celebrate the book’s fiftieth anniversary.