What is Visa policy of the United States?

The visa policy of the United States consists of the requirements for foreign nationals to travel to, enter, and remain in the United States. Visitors to the United States must obtain a visa from one of the U.S. diplomatic missions unless they come from one of the visa-exempt or Visa Waiver Program countries. The same rules apply for travel to all U.S. states, Washington, D.C., Puerto Rico and the U.S. Virgin Islands, as well as to Guam and the Northern Mariana Islands with additional waivers, while similar but separate rules apply to American Samoa.