Following an overview of the historiography on the origins and social reproduction of local populations in central Kenya, and on the Kikuyu in particular, this article analyses how the British colonial administration constructed concepts of "tribe" and "ethnicity" and the way that local groups then reappropriated them. The deconstruction of these ethnological concepts prompted Anglo-Saxon anthropology to develop the notion of ethnicity. The author then analyses the subsequent development of a catalogue of identities ("registre identitaire") among the Kikuyu and the way that it has shaped their society in the twentieth century. Finally, the conclusion emphasizes how this ethnic register has led to political polarization in contemporary Kenya and its consequences.