||The 5th SMOS Science Workshop Background The Soil Moisture and Ocean Salinity Mission is ESAs 2nd Earth Explorer Opportunity mission. It is an ESA led mission with contributions from the French Space Agency and the Spanish CDTI. The SMOS Project is currently in phase CD for a launch in February 2007. The SMOS satellite will provide, for the first time, direct measurements of Sea Surface Salinity and surface soil moisture thanks to its payload: a L-band Polarised interferometric radiometer. More recently, two other missions, with synergistic goals and approaches, Hydros and Aquarius, have been selected by NASA. Goals Consequently, after 4 successful SMOS science workshops since 1999 (see http://www.cesbio.ups-tlse.fr/us/indexsmos.html) and a joint Aquarius SMOS Hydros workshop held earlier this year, it is necessary to start addressing key points so as to proceed through SMOS phase C/D and prepare phase E.