"This Council Special Report addresses the economic logic of the current high levels of illegal immigration. The aim is not to provide a comprehensive review of all the issues involved in immigration, particularly those related to homeland security. Rather, it is to examine the costs, benefits, incentives, and disincentives of illegal immigration within the boundaries of economic analysis. From a purely economic perspective, the optimal immigration policy would admit individuals whose skills are in shortest supply and whose tax contributions, net of the cost of public services they receive, are as large as possible. Admitting immigrants in scarce occupations would yield the greatest increase in U.S. incomes, regardless of the skill level of those immigrants. In the United States, scarce workers would include not only highly educated individuals, such as the software programmers and engineers employed by rapidly expanding technology industries, but also low-skilled workers in construction, food preparation, and cleaning services, for which the supply of U.S. native labor has been falling. In either case, the national labor market for these workers is tight, in the sense that U.S. wages for these occupations are high relative to wages abroad ... This analysis concludes that there is little evidence that legal immigration is economically preferable to illegal immigration. In fact, illegal immigration responds to market forces in ways that legal immigration does not. Illegal migrants tend to arrive in larger numbers when the U.S. economy is booming (relative to Mexico and the Central American countries that are the source of most illegal immigration to the United States) and move to regions where job growth is strong. Legal immigration, in contrast, is subject to arbitrary selection criteria and bureaucratic delays, which tend to disassociate legal inflows from U.S. labor-market conditions. Over the last half-century, there appears to be little or no response of legal immigration to the U.S. unemployment rate. Two thirds of legal permanent immigrants are admitted on the basis of having relatives in the United States. Only by chance will the skills of these individuals match those most in demand by U.S. industries. While the majority of temporary legal immigrants come to the country at the invitation of a U.S. employer, the process of obtaining a visa is often arduous and slow. Once here, temporary legal workers cannot easily move between jobs, limiting their benefit to the U.S. economy"--Page 3-5.