Los Alamos National Laboratory (LANL) mainly exists as a place for the development of nuclear weapons. Like Oak Ridge, Tennessee, the town of Los Alamos was founded as a place for scientists and technicians to work on developing bombs in relative seclusion; when the first atomic weapons were being built, the seclusion was actually pretty extreme.
Los Alamos remains a key facility in the nuclear weapons complex. All of the work involving Plutonium is conducted at Los Alamos. Often, scientists at LANL devise experiments which are then conducted at the Nevada National Security Site (NNSS).