The L1 visa is a non-immigrant visa that allows foreign workers in managerial or specialized knowledge roles to transfer to a U.S. office of their employer, with two main types: L1A for managers (valid for up to 7 years) and L1B for employees with specialized knowledge (valid for up to 5 years). Key benefits include a pathway to permanent residency, familial inclusion, and no annual caps on visas issued. The application process involves proving the qualifying relationship between the U.S. and foreign companies, and there are specific documentation requirements for both employers and employees.