Generally, a citizen of a foreign country who wishes to enter the United States must first obtain a visa. Visitor visas are nonimmigrant visas for persons who want to enter the United States temporarily for tourism (visa category B-2).
Visa Waiver Program (VWP)
The VWP enables most citizens or nationals of participating countries* to travel to the US for tourism or business for stays of 90 days or less without obtaining a visa. In order to travel without a visa on the VWP, you must have authorization through the Electronic System for Travel Authorization (ESTA) prior boarding a US bound air or sea carrier.
Andorra, Australia, Austria, Belgium, Brunei, Chile, Croatia, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Japan, Latvia, Liechtenstein, Lithuania, Luxembourg, Malta, Monaco, Netherlands, New Zealand, Norway, Poland, Portugal, San Marino, Singapore, Slovakia, Slovenia, South Korea, Spain, Sweden, Switzerland, Taiwan*, United Kingdom**.