Although previous research has identified differences in the gender pay gap by employment sector, existing research on the causes of employer variation in the gender pay gap, particularly in the U.S. Federal Government, is limited (Smith-Doerr et al. 2019; U.S. Government Accountability Office 2020). This dissertation fills that gap by exploring organizational characteristics contributing to varying inequality regimes (Acker 2006) and subsequent pay equity variation. Using a linked employer-employee administrative dataset covering over 2 million federal employees, I measured governmentwide and agency-level gender pay gaps and explored organizational characteristics that explain agency-level differences. I found a governmentwide gross gender pay gap of 7.4%, but gender explained only 0.8% of the variation in logged salary. Workplace (agency) segregation explained 17.8% of the gross pay gap. However, including detailed occupational fixed effects in regression models explained far more of the salary variation than agency. The final governmentwide model, controlling for human capital, geography, agency, occupation, and occupation within agency, explained 84.9% of variation in logged salary and found a 3.0% within-job pay gap. Next, I calculated the gender pay gap net of explanatory factors for 371 federal agencies. In the average agency, the gross pay gap was 8.9%. Agencies’ gross, human capital/geography-controlled, and within-job pay gaps varied widely (within-job gaps of -12.4% to +12.4%), but 93% of agencies’ within-job pay levels favored men. Further, occupational segregation’s contribution to the pay gap varied from a 35.0% pay penalty for women to a 13.2% pay bonus. Finally, I explored whether pay plan segregation, women’s participation in management, racial/ethnic minority participation in management, and being part of the Department of Defense (DoD) were associated with between-job and within-job agency-level gender pay gaps. Supporting the concept of inequality regimes, women’s participation in management was positively correlated with women’s between-job and within-job relative pay, but less so in contexts that may decrease women managers’ power. Further, these contexts affect between-job and within-job pay gaps differently. In sum, the gender pay gap is context dependent. To improve pay equity, organization-specific solutions are needed.