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Generally, a citizen of a foreign country who wishes to enter the United States must first obtain a visa, either a nonimmigrant visa for temporary stay or an immigrant visa for permanent residence. Citizens of qualified countries may be able to visit the United States without a visa under the Visa Waiver Program. All travelers coming to the United States under the Visa Waiver Program must obtain authorization through the Electronic System for Travel Authorization (ESTA) system prior to initiating travel to the United States.
If you do not qualify for the Visa Waiver Program or are traveling to study, work, participate in an exchange program, or any other purpose that does not fall under a B visa purpose of travel; you will need a nonimmigrant visa. Also, if you are a citizen of a Visa Waiver Program country and your ESTA authorization was not approved, you will need to apply for a nonimmigrant visa.
A visa does not guarantee entry to the United States. A visa simply indicates that a U.S. consular officer has determined that you are eligible to apply for entry to the United States for a specific purpose.
A nonimmigrant visa is used by tourists, business people, students, or specialty workers who wish to stay for a particular period of time in the United States to accomplish specific purposes. According to U.S. visa laws and regulations, most nonimmigrant visa applicants must demonstrate to the consular officer that they have strong ties to their country of residence and must show that they intend to depart the United States after their temporary stay.