Los Alamos Ranch School was a private ranch school for boys in the northeast corner of Sandoval County, New Mexico, USA, founded in 1917 near San Ildefonso Pueblo. During World War II, the school was bought and converted into the secret nuclear research campus for Project Y, which later became the Los Alamos National Laboratory. The surrounding location has developed into the town of Los Alamos.

The Los Alamos Laboratory, also known as Project Y, was a secret laboratory established by the Manhattan Project and operated by the University of California during World War II. Its mission was to design and build the first atomic bombs. Robert Oppenheimer was its first director, serving from 1943 to December 1945, when he was succeeded by Norris Bradbury. In order to enable scientists to freely discuss their work while preserving security, the laboratory was located on the isolated Pajarito Plateau in Northern New Mexico. The wartime laboratory occupied buildings that had once been part of the Los Alamos Ranch School.