The NRAO 12 Meter Telescope began as the 36 Foot Telescope, the telescope responsible for the birth of millimeter-wavelength molecular astronomy. During a period of explosive growth in this new area of astronomical research dozens of molecular species known to exist in the interstellar medium were first detected at the 36 Foot. In 1984, the telescope's reflecting surface and surface support structure were replaced and the 36 Foot was re-christened the 12 Meter. Subsequently, the scientific program has evolved from one dominated by observing programs in astrochemistry to one with a broader mix of studies of molecular clouds and Galactic star formation, evolved stars, astrochemistry, and external galaxies. The 12 Meter is the only millimeter-wavelength telescope in the U.S. operated full-time as a national facility. More than 150 visitors make use of the telescope annually. It offers users flexibility and the opportunity to respond quickly to new scientific developments. The Observatory maintains low-noise receiving systems covering all atmospheric windows form 68 GHz to 300 GHz. Operational reliability throughout is emphasized. Flexible spectral line and continuum backends allow the observer to match the instrument to the scientific goals. The development of multi-beam receivers and the new on-the-fly observing technique has inaugurated a new era of high-speed source mapping on angular scales complementary to those of the millimeter-wave interferometers. The telescope control system offers great flexibility, efficiency, and convenience, and provides a proven remote observing capability.