Public sector employment of immigrants can increase their economic assimilation and potentially improve their treatment by government. Yet, as we show using Census data from 1990, 2000, and 2009-11, immigrants are substantially under-represented in federal, state, and local governments. To understand why, we use logit analysis for federal and for state and local government employment in each time period to test whether immigrants’ weaker educational attainment and English proficiency, lower probabilities of being citizens and military veterans, and different age, gender, and race/ethnicity distributions can explain that under-representation. Disparities in education and preferential government treatment of veterans are factors, but citizenship requirements appear to be the major obstacle to immigrant employment in the public sector.