Los Alamos National Laboratory (often shortened as Los Alamos and LANL) is one of the sixteen research and development laboratories of the United States Department of Energy (DOE), located a short distance northwest of Santa Fe, New Mexico, in the American southwest. Best known for its central role in helping develop the first atomic bomb, LANL is one of the world's largest and most advanced scientific institutions.

Los Alamos was established in 1943 as Project Y, a top-secret site for designing nuclear weapons under the Manhattan Project during World War II. Chosen for its remote yet relatively accessible location, it served as the main hub for conducting and coordinating nuclear research, bringing together some of the world's most famous scientists, among them numerous Nobel Prize winners. The town of Los Alamos, directly north of the lab, grew extensively through this period.

After the war ended in 1945, Project Y's existence was made public, and it became known universally as Los Alamos. In 1952, the Atomic Energy Commission formed a second design lab under the direction of the University of California, Berkeley, which became the Lawrence Livermore National Laboratory (LLNL). The two labs competed on a wide variety of bomb designs, but with the end of the Cold War, have focused increasingly on civilian missions. Today, Los Alamos conducts multidisciplinary research in fields such as national security, space exploration, nuclear fusion, renewable energy, medicine, nanotechnology, and supercomputing.

While owned by the federal government, LANL is privately managed and operated by Triad National Security, LLC.