This book examines estimates of fiscal impacts to the federal, state, and local governments of the foreign born who reside in the United States. It examines the academic and policy literature on fiscal impacts of two populations: all U.S. foreign born and unauthorised aliens. Computing such fiscal impacts involves numerous methodological and conceptual challenges, and resulting estimates vary considerably according to the assumptions used, including those about the time frame considered, the treatment of U.S.-born children, the unit of analysis used, and which costs and revenues are included.