Visa Waiver Program
The United States has a Visa Waiver Program (VWP) which allows eligible citizens of 36 participating countries to travel to the U.S. for tourism or business for a period of 90 days or less without obtaining a visa.
VWP travelers are required to have a valid authorization through the Electronic System for Travel Authorization (ESTA) prior to travel. An approved ESTA is required to enter the United States and is generally valid for two years, or until the passport expires, and allows multiple entries into the U.S. VWP travelers are screened at the port of entry into the United States, and are enrolled in the Department of Homeland Security's US-VISIT program.
Detailed information about admissions and entry to the United States under the Visa Waiver Program can be found on the DHS Customs Border Protection website at Visa Waiver Program and Admission to the United States.