U.S. immigration policy is governed largely by the Immigration and Nationality Act (INA), which was first codified in 1952 and has been amended significantly several times since. At a fundamental level, U.S. immigration policy can be viewed as two sides of a coin. One side emphasises the faciliation of migration flows into the United States according to principles of admission that are based upon national interest. These broad principles currently include family reunification, labor market contribution, humanitarian assistance, and origin-country diversity. The other side of the immigration policy coin emphasises the restriction of entry to and removal of persons from the United States who lack authorisation to reside in the country, are identified as criminal aliens, or whose presence in the United States is not considered to be in the national interest. The dual role of U.S. immigration policy creates challenges for balancing major policy priorities, such as ensuring national security, facilitating trade and commerce, protecting public safety, and fostering international co-operation.