The United States has always relied on immigrant workers, but in the last few decades their numbers have risen to a new peak. By 2000, roughly one in eight U.S. workers, or 17 million people, were foreign-born. That's up from about one in 17 in 1960, according to the U.S. Department of Labor. From 1996 to 2000, thanks to the economic boom, the number of jobs in the United States rose by 6.7 million; immigrants filled just under half of those. Pay scales typically follow this hierarchy: native-born American citizens, naturalized American citizens, legal immigrants and permanent residents, guest workers and finally undocumented workers. Overall, foreign-born workers earned about 76 cents for every dollar earned by U.S.-born workers in 2000.