The Electronic System for Travel Authorization (ESTA) is an automated system used to determine the eligibility of visitors to travel to the United States under the Visa Waiver Program (VWP) and whether such travel poses any law enforcement or security risk. Approved ESTA applications are valid for a period of 2 years, or until the passport expires, whichever comes first, and multiple trips to the United States without the traveler having to re-apply for another ESTA. When traveling to the U.S. with the approved ESTA, you may only stay for up to 90 days at a time.More information.