Who registers to vote? Although extensive research has examined the question of who votes, our understanding of the determinants of political participation will be limited until we know who is missing from the voter register. Studying voter registration in lower-income settings is particularly challenging due to data constraints. We link the official voter register with a complete social network census of 16 villages to analyze the correlates of voter registration in rural Uganda, examining the role of individual-level attributes and social ties. We find evidence that social ties are important for explaining registration status within and across households. Village leaders—and through them, household heads—play an important role in explaining the registration status of others in the village, suggesting a diffuse process of social influence. Socioeconomic factors such as income and education do not explain registration in this setting. Together these findings suggest an alternate theory of participation is required.