Immigration to the United States has fluctuated considerably over the course of the nation's history and has elicited various policy responses at different times. In recent years, concern about undocumented, illegal immigration has given rise to efforts to reform immigration law. The Immigration Reform and Control Act (IRCA) of 1986 was intended to stem the flow of undocumented immigrants into the United States, to reduce the number of illegal aliens already here, and to make provisions for various groups of transient workers. The major features of IRCA include the following: (1) employer sanctions penalizing employers who knowingly hire illegal immigrants; (2) a legalization program providing amnesty for undocumented immigrants who meet certain requirements; (3) a program for H-2 temporary foreign workers and seasonal agricultural workers; and (4) increased enforcement capabilities. Indicators of the effectiveness of IRCA include preliminary data on the amnesty program, employer sanctions, and border apprehensions. IRCA faces the following five emerging challenges: (1) domestic economic expansion and tightening U.S. labor markets; (2) projected rapid growth in service occupations; (3) declining size of U.S. youth cohorts; (4) mounting labor pressures in the Caribbean Basin; and (5) enforcement and compliance issues. The report includes statistical data on one graph and two tables. A list of 42 references is appended. (AF)