This paper examines whether the relatedness of populations across the world shapes international trade flows. Using data on common ancestry for 172 countries covering more than 99% of global trade, we document that country pairs with weaker ancestral relationships are less likely to trade with each other (extensive margin) and, if they do trade, they exchange fewer goods and smaller volumes (intensive margin). The effect of ancestry is robust to a vast array of micro geographic control variables and mitigated, yet still sizable and significant, when controlling for other measures of cultural distance as well as for current migrant stocks.