"Daniel Posner here offers a powerful new theory of ethnic politics that combines institutionalist and rationalist approaches to social science with a social constructivist approach to ethnic identity. Drawing on an analytical model of ethnic identities and coalitions, Posner shows how institutions shape ethnic identities. Over decades, institutions narrow a wide range of potential ethnic identities to a set of politically salient identities. In the short run, institutions determine which of those salient identities are the basis of mobilization and voting. Drawing on a natural experiment in Zambia where electoral rules changed from multi-party political competition to one-party rule and back again, Posner demonstrates the power of this theory. The result is a sophisticated work that combines field research, institutionalist and constructivist theory, and data analysis -- in short, a must read for scholars of ethnic politics and comparative social science." -Elisabeth Jean Wood, Yale University