International labor mobility has its benefits in the global economy, particularly for those who succeed at getting higher-wage jobs in developed nations than those they could get in their own less-developed homeland, but it also leads to significant problems in terms of whether those workers are working according to the laws and rules of the host country. Most nations attempt to reduce the problem of illegal workers through border patrols and internal enforcement, and early studies have shown them to be of uncertain value. Here, the authors refine these studies and examine the effects of enforcement on both the host and foreign countries, examining the welfare of border and internal enforcement and locating an optimal level for internal reinforcement. They offer this information necessary for immigration authorities to carry out internal enforcement beneficial to states both providing and receiving illegal workers. Annotation ©2006 Book News, Inc., Portland, OR (booknews.com)