Visas allow foreign nationals to travel to the US for particular purposes, including:
Tourism.
School.
Employment.
Permanent relocation.
Visas may only be used while they are valid. They are issued for a duration determined by both:
The classification requested.
The foreign national's citizenship.
Some visas need advance US Citizenship and Immigration Services (USCIS) approval before they can be issued. Visas may expire or be cancelled. For more information, see: