This paper examines the significance of ethnicity as a political cleavage across African nations over time. While scholars have studied the influence of ethnicity in structuring party politics in Africa, those studies have largely been limited to an examination of ruling party support. This work develops a measure of ‘ethnic voting’ that is reflective of all significant parties and ethnic groups. This measure of ‘ethnic voting’ allows us to compare reliably across countries within the Afrobarometer sample. Adopting measures that have been employed in class analyses in developed countries over the past twenty years, we construct two measures,‘ethnic polarization’ and ‘ethnic diversity’. The former captures the importance of ethnicity in determining party support levels while the latter captures variations in the ethnic diversity of the support base of different parties. Together, these two measures show variation in the salience of ethnicity as a political cleavage across African countries over time.