There are two channels for obtaining permission to work in the United States: nonimmigrant work visas and immigrant work visas. Nonimmigrant visas confer temporary authorization to work in the U.S., while immigrant visas grant permanent residence to live and work in the U.S. long-term. As a general rule of thumb, nonimmigrant work visas typically require employer sponsorship, meaning a U.S. company must file for the visa on behalf of the foreign national. Immigrant visas, or Green Cards, are designed for employees working in identified occupations in which U.S. workers are in short supply.