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. Visitor visas are nonimmigrant visas for persons who want to enter the United States temporarily for business (visa category B-1), tourism, pleasure or visiting (visa category B-2), or a combination of both purposes (B-1/B-2).
There are several steps to apply for a visa. The order of these steps and how you complete them may vary at the U.S. Embassy or Consulate where you apply.
A visa allows a foreign citizen to travel to a U.S. port-of-entry (generally an airport) and request permission to enter the United States. A visa does not guarantee entry into the United States. The Department of Homeland Security (DHS), U.S. Customs and Border Protection (CBP) officials at the port-of-entry have authority to permit or deny admission to the United States. If you are allowed to enter the United States, the CBP official will provide an admission stamp or a paper Form I-94, Arrival/Departure Record.
You must depart the United States on or before the date indicated on your admission stamp or paper Form I-94, unless your request to extend your stay is approved by USCIS.
Failure to depart the United States on time will result in you being out of status. Under U.S. law, visas of travelers who are out of status are automatically voided (Section 222(g) of the Immigration and Nationality Act). If you had a multiple-entry visa and it was voided due to you being out of status, it will not be valid for future entries into the United States.
Failure to depart the United States on time may also result in you being ineligible for visas you may apply for in the future.
While in the United States, you may be able to request that U.S. Citizenship and Immigration Services (USCIS) change your nonimmigrant status to another nonimmigrant category.
Requesting a change of status from USCIS while you are in the United States and before your authorized stay expires does not require that you apply for a new visa. However, if you cannot remain in the United States while USCIS processes your change of status request, you must apply for a visa at a U.S. Embassy or Consulate.