The Allen Telescope Array (ATA) is a centimeter-wavelength radio telescope producing unique science in the areas of radio surveys and transient source detection. The ATA is the first radio telescope designed for commensal observing; it will simultaneously produce sensitive SETI (Search for Extraterrestrial Intelligence) surveys as well as large area continuum and spectroscopic surveys for conventional radio astronomy. The science of the ATA is enabled by a number of innovative technical developments. The ATA may serve as a prototype for the US design of the Square Kilometer Array (SKA), a next generation radio telescope currently in the planning phase. Located in Hat Creek, CA, formerly the site of the Berkeley Illinois Maryland Association (BIMA) millimeter-wavelength array, the ATA currently consists of 42 offset Gregorian antennas with continuous frequency response from 0.5 to 11.2 GHz, with the possibility of future upgrades to more antennas.