work under a simplified procedure. Visa Waiver Program As of 2023, 40 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) prior to arrival. 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. The Electronic System for Travel Authorization (ESTA) is not considered a visa, but a prerequisite to traveling to the United States under the Visa Waiver Program. ESTA has an application fee of US$4, and if approved, an additional fee of $17 is charged, for a total of $21. Once obtained, the authorization is valid for up to two years or until the traveler's passport expires, whichever comes first, and is valid for multiple entries into the United States. Passengers are advised to apply for ESTA at least 72 hours before departure. Travel by air or sea with ESTA must be made on a participating commercial carrier. The VWP does not apply at all if arriving by air or sea on an unapproved carrier (e.g. a private ship or plane), in which case a standard visa is required. ESTA is also required for entry by land. As of 2023, those who have previously traveled to Iran, Iraq, Libya, North Korea, Somalia, Sudan, Syria or Yemen on or after March 1, 2011, or to Cuba on or after January 12, 2021, or who are dual nationals of Iran, Iraq, North Korea, Sudan or Syria, are not eligible to travel under the VWP and must obtain a standard visa. However, those who traveled to such countries as diplomats, military, journalists, humanitarian workers or legitimate businessmen may have this ineligibility waived. Visa waiver programs of Guam and the Northern Mariana Islands Although the visa policy of the U.S. also applies to the U.S. territories of Guam and the Northern Mariana Islands, both territories have additional visa waiver programs for certain nationalities. The Guam–CNMI Visa Waiver Program, first enacted in October 1988 and periodically amended, permits nationals from 12 countries in Asia, Europe and Oceania to enter Guam and the Northern Mariana Islands as tourists for up to 45 days without the need to obtain a U.S. visa