How does the representation of women in international organizations affect the implementation of gender mainstreaming policies? Many international organizations have adopted policies to prevent gender discrimination in their operations, but their implementation is often lackluster. We argue that these shortcomings appear due to a combination of institutional incentives and an underrepresentation of women in their staff. We test the argument in the case of the World Bank, drawing on highly disaggregated staffing data, an instrumental variable strategy, and an elite survey experiment. Our results show that most staff incorporate at least shallow gender mainstreaming in their projects. Deeper implementation of gender mainstreaming is more likely when women staff supervise projects, hold positions of authority, and are more represented as coworkers. These results contribute to understanding the disconnects between talk and action on mainstreaming policies and inform debates on representation in global governance.