Current uncertainties in the effects of aerosols and clouds on the Earth radiation budget limit our understanding of the climate system and the potential for global climate change. PICASSO-CENA is a recently approved satellite mission within NASA's Earth System Science Pathfinder (ESSP) program designed to address these uncertainties. The PICASSO-CENA payload includes a lidar and three passive instruments which will provide unique information on the global distribution and properties of aerosols and clouds. PICASSO-CENA will be flown in formation with the EOS PM and CloudSat satellites to provide coincident measurements of atmospheric state, radiative fluxes, and thick clouds. This global suite of measurements will provide a basis for improving the representation of clouds and aerosols in climate models, leading to improved capabilities for predicting climate and climate change. PICASSO-CENA is planned for a three year mission beginning in early 2003 and is being developed within the framework of a collaboration between NASA and CNES.