We use new matched employer-employee data to estimate the contributions of sex segregation and wage differences by sex within occupation, industry, establishment, and occupation-establishment cells to the overall sex gap in wages. In contrast to earlier data used to study this question, our data cover all industries and occupations across all regions of the United States. We find that segregation of women into lower-paying occupations, industries, establishments, and occupations within establishments accounts for a sizable fraction of the sex gap in wages.