The Gamma-ray Large Area Space Telescope, GLAST, is a satellite-based experiment under development to measure the cosmic gamma-ray flux in the energy range 20 MeV to 300 GeV (with acceptance up to 1 TeV). With a sensitivity that is more than a factor 30 greater than that of the EGRET detector on GRO, GLAST will open a new and important window on a wide variety of high energy phenomena, including supermassive black holes and active galactic nuclei, gamma-ray bursts, supernova remnants, and searches for new phenomena such as supersymmetric dark matter annihilations and big bang particle relics. The launch is planned for 2005. This talk will include a discussion of the physics, the instrument, the novel collaboration of particle physicists and high energy astrophysicists, and the mission status.