This paper proposes that major determinants of allocation of women's time are social norms that regulate the economic activities of women. Our emphasis on norms contrasts with approaches that view time allocation as determined by household-level economic variables. Using data from Burkina Faso, we show that social norms significantly explain differences in patterns of time allocation between two ethnic groups: Mossi and Bwa. Econometric results show women from the two groups exhibiting different responses to changes in farm capital. Implications are that policies that foster changes in social norms may have more permanent effects on altering women's behavior.