What is a Visa?
In general, citizens of foreign countries need a visa stamp in their passport to enter the United States the same way citizens of the U.S. may need a visa to enter a foreign country. Most foreign nationals interested in coming to the U.S. will need to apply for the appropriate visa at a U.S. Embassy or Consulate outside of the U.S. Exceptions are made for Canadian citizens and a designated list of countries (currently 27) eligible to visit the U.S. temporarily under the B1/B2 Visa Waiver Program.
Individuals who need to apply for a visa should be advised to apply in the country they currently reside or their citizenship country. Appointment arrangements and visa application processing times vary at each embassy. In addition, security clearances, especially in areas that are considered sensitive or are listed on the Technology Alert List, may cause unpredictable delays in the visa processing. While there is no way to control the visa processing time, especially in cases of individuals who may be subject to delays, ensuring the individual is prepared for the visa interview will significantly facilitate the visa processing.
F students and J Exchange Visitors (students, scholars, and researchers) must pay a $100 SEVIS I-901 fee prior to the visa appointment in addition to any visa issuance or reciprocity fees (based on the country of citizenship).
A visa doesn't permit entry to the U.S., however. A visa simply indicates that a U.S. consular officer at an American embassy or consulate has determined a foreign national is eligible to enter the country for a specific purpose. Consular affairs are the responsibility of the U.S. Department of State.
A visa allows you to travel to the United States as far as the port of entry (airport or land border crossing) and an immigration officer allows admission to the country. Only the immigration officer has the authority to permit you to enter the United States. He or she decides how long you can stay for any particular visit. Immigration matters are the responsibility of the U.S. Department of Homeland Security.
CATEGORIES OF VISA
Immigrant visas are for people who intend to live permanently in the U.S.
Nonimmigrant visas are for people with permanent residence outside the U.S. but who wish to be in the U.S. on a temporary basis - for tourism, medical treatment, business, temporary work, or pursue studies, among other things.