Early explanations for gender wage gaps focused on human capital or career choices. This column uses data from the US and ten European countries to examine the role of firms. Across all countries considered, firms account for between 10% and 30% of the gender wage gap, mainly reflecting women being more likely to work at firms that pay less to all employees, irrespective of their skills. While men move to higher-paying firms as they advance in their career, women tend to stay behind. Women also