This paper documents and studies the gender gap in performance among associatelawyers in the United States. Unlike other high-skilled professions, the legal professionassesses performance using transparent measures that are widely used and comparableacross firms: the number of hours billed to clients and the amount of new client revenuegenerated. We find clear evidence of a gender gap in annual performance with respectto both measures. Male lawyers bill ten percent more hours and bring in more thantwice the new client revenue than do female lawyers. We demonstrate that thedifferential impact across genders in the presence of young children and differences inaspirations to become a law firm partner account for a large share of the difference inperformance. We also show that accounting for performance has importantconsequences for gender gaps in lawyers earnings and subsequent promotion. Whereasindividual and firm characteristics explain up to 50 percent of the earnings gap, theinclusion of performance measures explains a substantial share of the remainder.Performance measures also explain a sizeable share of the gender gap in promotion.