Although the pay gap between men and women in the U.S. workforce has narrowed since the 1980s, numerous studies have found that a disparity still exists. In 2003, we found that women in the general workforce earned, on average, 20 cents less for every dollar earned by men in 2000 when differences in work patterns, industry, occupation, marital status, and other factors were taken into account. Other research indicates that this disparity existed for federal workers as well. For example, a 1998 study showed that the pay gap between men and women in the federal workforce decreased significantly between 1976 and 1995, but in 1995 white women still earned 14 cents less for every dollar earned by white men and African-American women earned 8 cents less for every dollar earned by African-American men after available factors related to pay were taken into account. In light of concerns that a pay gap may continue to exist between men and women in the workplace, Congress asked us to examine pay disparity issues and the role the federal government has played in enforcing anti-discrimination laws. In agreement with Congressional staff, we addressed these questions in two separate, consecutive reports, the first of which focused on enforcement and outreach efforts in the private sector and among federal contractors. This second report addresses the following question: To what extent has the pay gap between men and women in the federal workforce changed over the past 20 years and what factors account for the gap? To answer this question, we used two approaches to analyze data from the Central Personnel Data File (CPDF)--maintained by the Office of Personnel Management (OPM)--covering a 20-year period. First, we looked at "snapshots" of the federal workforce at three points in time (1988, 1998, and 2007) to show changes in the federal workforce over a 20-year period. Second, we examined the cohort (or group) of employees who joined the federal workforce in 1988 and tracked their careers over the course of 20 years to look for differences in the pay gap in this group. We used CPDF data to generate summary statistics on the federal workforce and to perform multivariate analyses, which we used to identify the amount of the gender pay gap attributable to differences in measurable factors--such as work-related and demographic characteristics of men and women. To further inform our analyses, we reviewed existing literature and reports on gender and pay and interviewed officials at the Office of Personnel Management and the Equal Employment Opportunity Commission (EEOC).