Pursuant to U.S. immigration law, an alien, in order to enter legally into the US, must not belong to one of the "grounds of exclusion" unless the ground of exclusion is waivable and he/she actually obtains a waiver.

General grounds for exclusion are:

• Medical (communicable diseases, addictions, mental disorders, etc.)
• Criminal (persons convicted of certain crimes, or number of convictions, drug traffickers, etc.)
• Security (terrorists, totalitarians, etc.)
• Public Charge (persons likely to become public charges in the US)
• Labor (Person´s seeking work without approved labor certification)
• Illegal Entrants and Immigration Violators
• Documentation Requirements (Persons not in possession of valid immigration documents)
• Ineligible for Citizenship (Person´s permanently ineligible for citizenship or Draft Evaders)
• Miscellaneous (Polygamists, guardians of excluded child, child abductors)