Of the 40 million foreign-born people living in the United States in 2011, about 22 million were not citizens. About half of those noncitizens were authorized to be in the United States either temporarily or permanently; the remainder, about 11.5 million people, were in the country without authorization, a number that has changed little over the past few years. Noncitizens tend to differ from both foreign- and native-born citizens in several ways, especially in terms of their skills and employment status, which can have important effects on government revenues and spending. CBO analyzes trends in immigration and policy proposals that would affect immigration.