The Defense Language Institute, also known as DLI, is a United States Department of Defense (DoD) educational and research institution. The first classes began on November 1, 1941, with only four instructors and just 60 students in a deserted airplane hangar at Crissy Field. DLI provides linguistic and cultural training to the Department of Defense, other Federal Agencies and several other customers.

The main responsibility of the Defense Language Institute is the Defense Language Program, and educating DoD members in assigned languages. The other activities include planning, curriculum development, and research in second-language acquisition. The members of other Federal agencies may also receive training in this institute.