We build a consistent measure of male and female work for the US for the period 1880-2019 - encompassing intensive and extensive margins - by combining data from the US Census and several early sources. The resulting measure of hours, including paid work as well as unpaid work in family businesses, displays an asymmetric U-shape for women, with a modest decline up to mid-20th century and a sustained rise afterwards. For men, hours fall throughout the sample period. We empirically and theoretically relate these trends to the process of structural transformation, and namely the reallocation of labour across agriculture, manufacturing and services, and the marketization of home production. We propose a multisector model of the economy with uneven productivity growth, income e ects, and consumption complementarity across sectoral outputs. At early stages of development, declining agriculture leads to rising services (both in the market and the home) and leisure, implying a fall in market work for both genders. At later stages of development, structural transformation reallocates labor from manufacturing into services, and a large service economy implies an important marketization process, progressively reallocating work from home to market services. Given gender comparative advantages, the first channel is more relevant for men, implying a decrease in male hours, and the second channel is more relevant for women, implying an increase in female hours.