This paper draws on data from over 33,000 respondents in twenty-two surveys in ten African countries to investigate the political sources of ethnic identification in Africa. We find strong evidence that the strength of ethnic identities in Africa is shaped by political competition. In particular, we find that respondents are more likely to identify in ethnic terms the closer their country is to a competitive presidential election. Exposure to political competition, as well as non-traditional occupations, powerfully affects whether or not people identify themselves in ethnic terms. This finding is consistent with the view that ethnic identities in Africa are not “in the blood” but both malleable and subject to instrumental manipulation by politicians. Taken together the findings provide strong confirmation for what we term “second wave” modernization approaches to ethnicity, and for theories that link the salience of particular social identities to instrumental political mobilization. Beyond their relevance for these academic literatures, the paper’s results also have important implications for policymakers and researchers interested in ethnicity’s effects.