Recent advances in theory and observations using passive microwave remote sensing have hightlighted the potential of spaceborne sensors for contributing to the required land surface measurements of soils, vegetation, snow cover and precipitation. Furthermore, the spatial resolution of passive microwave observations matches the special scales of large-scale models of land-atmosphere interactions both for data assimilation and validation. In order to stimulate and focus this research a workshop, sponsored by ESA and NASA, was organized to review the state-of-the-art in microwave radiometry related to land applications and to exchange ideas leading into new directions for future research. This volume contains the refereed papers from the aforementioned ESA/NASA workshop, which are arranged by topic, as well as the (edited) working group reports.