As of 2021, 39 countries have been selected by the U.S. government for inclusion in the Visa Waiver Program (VWP). Their nationals do not need a U.S. visa for short stays, but they are required to obtain an electronic authorization (ESTA) for arrivals by air or sea. Visitors may stay for up to 90 days in the United States, which also includes time spent in Canada, Mexico, Bermuda or the islands in the Caribbean if the arrival was through the United States.