While gender gaps in political participation are pervasive, especially in developing countries, this study provides systematic evidence of one cultural practice that closes this gap. Using data from across Africa, this article shows that matrilineality – tracing kinship through the female line – is robustly associated with closing the gender gap in political participation. It then uses this practice as a lens through which to draw more general inferences. Exploiting quantitative and qualitative data from Malawi, the authors demonstrate that matrilineality's success in improving outcomes for women lies in its ability to sustain more progressive norms about the role of women in society. It sets individual expectations about the gendered beliefs and behaviors of other households in the community, and in a predictable way through the intergenerational transmission of the practice. The study tests and finds evidence against two competing explanations: that matrilineality works through its conferral of material resources alone, or by increasing education for girls.