This article draws on data from over 35,000 respondents in 22 public opinion surveys in 10 countries and finds strong evidence that ethnic identities in Africa are strengthened by exposure to political competition. In particular, for every month closer their country is to a competitive presidential election, survey respondents are 1.8 percentage points more likely to identify in ethnic terms. Using an innovative multinomial logit empirical methodology, we find that these shifts are accompanied by a corresponding reduction in the salience of occupational and class identities. Our findings lend support to situational theories of social identification and are consistent with the view that ethnic identities matter in Africa for instrumental reasons: because they are useful in the competition for political power.