The Taiwan/US satellite mission COSMIC (Constellation Observing System for Meteorology, Ionosphere, and Climate) is in preparation for launch in late 2005. COSMIC will launch 6 satellites into 6 orbital planes. The orbits will be circular at 800-km altitude, with 72-degree inclination, and 24-degree separation in ascending node. Each satellite will carry three atmospheric science payloads: (1) a GPS occultation receiver for ionospheric and neutral atmospheric profiling and precision orbit determination; (2) a Tiny Ionospheric Photometer (TIP) for monitoring the electron density via nadir radiance measurements along the sub-satellite track; and (3) a three-frequency Beacon transmitter for ionospheric tomography and scintillation studies. Signals from occulting GPS satellites are received on the COSMIC satellites to profile the ionospheric electron density from orbital altitude (800 km) through the F2 layer and the E layer with about 1.5 km vertical resolution. As the GPS satellite sets further the occulting signals are used to profile atmospheric refractivity from ~40 km to the surface with vertical resolution of a few hundred meters. The TIP data will be combined with the GPS observations for improved ionospheric profiling in regions of large horizontal electron density gradients on the night-side. Thus COSMIC will deliver ~2500 atmospheric occultation profiles per day from near the surface to 800 km altitude. These data will be used in numerical weather prediction and for space weather models. This presentation will provide an overview of the COSMIC mission and present example space weather results from past and present radio occultation missions.