The National Radio Astronomy Observatory Green Bank Telescope (GBT), the world's largest fully steerable telescope, is now undergoing commissioning and early scientific operation. The GBT has many innovative design features that advance imaging quality, sensitivity, and versatility. These include an unblocked aperture, an active surface, and a six-degree of freedom Gregorian subreflector. The GBT has an advanced laser rangefinder metrology system, which will measure the position of the active surface panels, and also guide the precision pointing of the telescope. Early commissioning results have confirmed the performance of the telescope, and exciting scientific discoveries are already being made. This paper describes the various features of the telescope in more detail, and presents the latest results.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.