The Visa Waiver Program (VWP) allows most citizens of participating countries to travel to the United States for tourism or business for stays of 90 days or less without first obtaining a visa, when they meet all VWP requirements.
Travelers must have a valid Electronic System for Travel Authorization (ESTA) approval prior to travel. ESTA will determine, in many cases almost immediately, if an individual is eligible for VWP travel, and if such travel poses any law enforcement or security risks. To facilitate the authorization process, DHS recommends that ESTA applications be submitted as soon as an applicant begins planning U.S.-bound travel, and not less than 72 hours prior to travel.
Please visit the Travel.State.gov Visa Waiver Program page for the list of participating countries, information about ESTA, and the full list of requirements.