 Soil moisture has recently been added to the list of essential climate variables, ECVs, which are deemed essential for IPCC and UNFCCC needs and considered feasible for global observation. To create a consistent data record, multiple data sources including active and passive microwave observations in the low-frequency range should be used, with sensors such as C-band scatterometers on ERS and METUP satellites and multi-frequency radiometers. The best approach for fusing these data sets is to merge level 2 soil moisture data derived from individual satellite data records, which has already been demonstrated in the WACMOS project and will be further improved in the Climate Change Initiative program of ESA. This article was authored by W. Wagner, W. Derigo, Ardezure and others.