Generally speaking, unless they're from Europe or certain Asian countries, all international travelers will need visas to enter the United States. Visas are issued by the U.S. Department of State.
The United States does not require visas from citizens of 37 countries provided they stay no longer than 90 days and they do not work or study. Visas are required for all journalists regardless of their citizenship. Citizens of all European countries, as well as Brunei, Japan, Taiwan, Singapore, New Zealand, South Korea and Australia, do not need visas whether traveling for pleasure, business or medical treatment.
Travelers who qualify for the Visa Waiver Program still need approval to travel here through the Electronic System for Travel Authorization (ESTA)program that is administered by the U.S. Department of Homeland Security's Customs and Border Patrol division. ESTA forms require biographical information from the applicant. Applications can be filled out online and a fee is charged; fact sheets are available in 10 languages besides English. Once approved, ESTA is good for two years for as many trips as travelers make in this time.
All other visitors who do not qualify for the Visa Waiver Program must obtain a visa. The type of visa required depends on the nature of the visit. For example, athletes and business visitors need a B-1 visa while visitors coming for tourism need a B-2 visa. Canadian citizens do not need visas or ESTA approval to enter the United States, though they should have their passports with them.
Visa applications are available online and can also be obtained at any U.S. embassy or consulate abroad. Photographs, with specific requirements, are required as part of the application process. The visa application fee depends on the applicant's country of citizenship. Completed applications are submitted at embassies and consulates as applicants are required to have a personal interview. The State Department asks prospective visitors to check with the embassy or consulate for interview wait times as well as for any local procedures or instructions. The department maintains a list of websites for U.S. embassies and consulates throughout the world.