A historical data set of continuous satellite derived global land surface moisture and land surface temperature is being developed jointly by the NASA Goddard Space Flight Center and the Vrije Universiteit Amsterdam. The data will consist of surface soil moisture retrievals from observations of both historical and currently active satellite microwave sensors, including Nimbus-7 SMMR, DMSP SSM/I, TRMM TMI, and AQUA AMSR-E. The data sets will span the period from November 1978 through December 2005. The soil moisture retrievals are made with the Land Parameter Retrieval Model, which was developed jointly by researchers from the above institutions. The various sensors have some different technical specifications, including primary wavelength, radiometric resolution, and frequency of coverage. Consequently, the soil moisture sensing depth also varies between the different sensors. It is expected that the data will be made available for download by the general science community within about six months. Specifications and capabilities of different sensors and how they affect soil moisture retrievals are discussed.