Four major principles currently underlie U.S. policy on legal permanent immigration: the reunification of families, the admission of immigrants with needed skills, the protection of refugees, and the diversity of admissions by country of origin. These principles are embodied in federal law, the Immigration and Nationality Act (INA) first codified in 1952. The Immigration Amendments of 1965 replaced the national origins quota system (enacted after World War I) with per-country ceilings, and the statutory provisions regulating permanent immigration to the United States were last revised significantly by the Immigration Act of 1990. The critiques of the permanent legal immigration system today are extensive, but there is no consensus on the specific direction the reforms of the law should take. As the Congress considers comprehensive immigration reform (CIR), many maintain that revision of the legal immigration system should be one of the major components of a CIR proposal. This primer on legal permanent immigration law, policies, and trends provides a backdrop for the policy options and debates that may emerge as Congress considers a revision of the legal immigration system.