There is a widespread assumption that both ethnicity itself, and ethnic conflict, are inevitable. Yet, we know very little about how ethnic identifications function in bureaucratic terms in Africa. The stakes of this problem are rapidly escalating in moves to digital identification and population knowledge systems. Focusing on Kenya, this study provides an urgently needed exploration of where ethnic classifications have come from, and where they might go. Through genealogies of tools of ethnic identification - maps, censuses, ID cards and legal categories for minorities and marginalised communities - Samantha Balaton-Chrimes challenges conventional understandings of classifications as legible. Instead, she shows them to be uncertain and vague in useful ways, opening up new modes of imagining how bureaucracy can be used to advance pluralism. Knowing Ethnicity holds important insights for policy makers and scholars of difference and governmentality in postcolonial societies, as well as African and ethnic politics.