Is a visa always necessary for a foreign national to enter the United States?
In general, a visa is necessary. However, the one way for foreign nationals to enter the United States without a visa is the Visa Waiver Program (VWP). Under the VWP, foreigners from certain nations can enter the United States without first obtaining a visa. The U.S. Department of State’s Visa Waiver Program page maintains an updated list of nations that participate in this program. Foreign nationals who wish to enter the U.S. under the VWP must have an e-passport or machine-readable passport and an approved authorization through the Electronic System for Travel Authorization (ESTA). A visa under the VWP is valid for 90 days.
