The Gamma Ray Large Area Space Telescope (GLAST) is a high energy (20–300 GeV) gamma-ray astronomy mission planned for launch in 2005. The overarching scientific theme of the mission is studying sites of particle acceleration in the Universe. Topics of interest include active galactic nuclei and their jets, extragalactic and galactic diffuse emissions, dark matter, supernova remnants, pulsars, and the unidentified high energy gamma-ray sources. The sensitivity is 2 × 10 −9 photons cm −2 s −1 (>100 MeV) for a 2 year all-sky survey, which is a factor of >30 better than CGRO/EGRET. The GLAST program is currently in a high level of mission development activity.