The 4th Aquarius/SAC-D Science Workshop was held in Puerto Madryn, Chubut, Argentina on 3-5 December 2008. Sessions addressed calibration and validation and explored a range of scientific studies and practical applications, such as the global hydrological cycle, ocean circulation, climate variability, oceanic CO2 flux, land processes, land use, soil moisture, natural hazards, cryosphere, operational forecasting, among many others.This conference was held in honor of the late Dr. F. Raul Colomb, Principal Investigator for the CONAE SAC-C and SAC-D Missions.