A foreign national temporarily present in the United States who is not a resident alien. Nonresident aliens are taxed according to special rules contained in certain parts of the Internal Revenue Code. A “nonresident alien” will become a “resident alien” in one of two ways: (1) by being admitted to the U.S. as, or changing status to, a Lawful Permanent Resident under the Immigration Laws (the Green Card test); or (2) by passing the Substantial Presence Test (a numerical formula which measures days of presence in the U.S.). (26 USC 7701(b).)