Active technologies are now beginning to provide new satellite remote sensing capabilities, complementing those of passive sensors. Following the Lidar In-space Technology Experiment (LITE) on the Space Shuttle in 1994, and the Geoscience Laser Altimeter System (GLAS) in 2003, the CALIPSO satellite was launched in Spring 2006. CALIPSO is providing unique measurements to improve our understanding of the role of aerosols and clouds in the Earth's climate system. The primary instrument on CALIPSO is CALIOP (Cloud-Aerosol LIdar with Orthogonal Polarization), a two-wavelength polarization lidar. Using a linearly polarized laser and polarization-sensitive receiver, the instrument allows the discrimination of cloud ice/water phase and the identification of non-spherical aerosols. This talk will provide an overview of the CALIPSO mission and discuss initial performance assessments and results from CALIOP.