We use Demographic and Health Survey data to undertake the largest ever examination into the causes of inter-ethnic marriage in contemporary Sub-Saharan Africa and document a number of novel findings. First, we show that inter-ethnic marriage rates are high, at 19.4% on average, vary significantly across countries and are rising over time.Second, we show that individual variables associated with modernization such as urbanization, literacy/education and declines in polygamy and agricultural employment are correlated with inter-ethnic marriage. Third, we show that inter-ethnic marriage is quadratically correlated with ethnic group size and negatively correlated with both educational homogamy and country-population size.