This paper documents the gender gap in performance among high-skilled professionals in the United States. On the basis of widely used performance measures in law firms, we find that male lawyers bill 10 percent more hours and bring in more than twice as much new client revenue as female lawyers. The differential impact across genders in the presence of young children and differences in aspirations to become a law firm partner account for a large share of the difference in performance. We show that accounting for performance has important consequences for gender gaps in lawyers' earnings and subsequent promotion.