In situ soil moisture observations are crucial for validating land surface models andsatellite soil moisture retrievals. The proposed project will be performed in support of European Space Agency¿s (ESA) Soil Moisture and Ocean Salinity (SMOS) mission, also referred to as ESA¿s ¿Water Mission¿. This mission has the objectives to advance knowledge of the water cycle, its dynamics and the possible impact of climate change. Near-surface soil moisture will be derived from multi-angular, dual-polarisation L-band brightness temperature data reconstructed from SMOS interferometric observations. Yet, globally the number of long-term in-situ monitoring networks is small and mostly restricted to mid-latitude regions. Also, the properties of the data may vary significantly between networks given that there is neither a standard measurement technique nor a standard protocol. Therefore, significant international cooperation is required to collect and harmonize existing data sets and to establish new monitoring networks. The proposed project will support calibration and validation activities of the SMOS mission by setting up a database and web hosting system for disseminating homogenized data sets of in situ soil moisture measurements collected from various existing networks. Through this it will also support validation and calibration activities for other satellite sensors used for soil moisture retrieval (ASCAT, AMSR-E, Windsat, SMAP, ...).