Extensive research has focused on why people move from place to place without documentation. However, few studies have compared different types of immigration controls or their effectiveness in different countries. A framework for evaluating existing control measures needs to have a testable theoretical basis, to determine whether a control system fits the public and political disposition to punish a particular crime, to rate the efficiency of the control methods, and to measure variation from one location or time to another. Evaluation of three forms of immigration control in Belgium, the Netherlands, and the United States indicated that employer sanctions and border interdiction have some impact on the number of undocumented entrants to a particular country. However, refugee detention had little effect; reports conflicted regarding whether it deters or encourages additional undocumented migration. Field studies on the three methods also reveal substantial variation in the severity, uniformity of enforcement, clarity, and certainty of control. Tables, footnotes, and 28 references