A United States entry visa is an endorsement or stamp, placed by a United States Official, on a passport that allows the bearer to visit the United States . Any foreign person arriving at a port of entry seeking admission to the United States , as either an immigrant or nonimmigrant, must demonstrate admissibility pursuant to US visa law and policy. Such person must present documents, unusually a valid passport and appropriate visa, or other evidence for admission as required by the Department of Homeland Security (DHS) and submit to inspection by immigration officials.

Even United States citizens, lawful permanent residents, and other persons returning to the United States , after temporary travel abroad, are subject to the determination of admissibility upon arrival at a port of entry.

Nationals of approximately 27 countries designated under the Visa Waiver Program may enter the United States , without a visa, for periods up to 90 days as visitors for business or pleasure. No alien admitted without a visa, however, may be authorized to remain in the United States as a nonimmigrant visitor for a period exceeding 90 days from the date of admission.

Possession of a valid passport, and selection and acquisition of the best and most appropriate visa are key entry documents for any alien who desires to stay in the United States more than 90 days or engage in activities such as U. S. employment not usually allowed to visitors for business or pleasure. The United States Department of State (DOS) administers the visa issuance process for aliens who desire to come to the United States .

Any alien who desires to lawfully enter the United States must secure a visa at a US embassy or consulate, unless such person is visa exempt. The Immigration and Nationality Act (INA) prescribes the documents required for admission of both immigrants and nonimmigrants into the United States.