Soil moisture controls the physical processes that exchange mass and energy between the atmosphere and the land surface in the hydrologic cycle.Improved observations of soil moisture may lead to improvements in weather forecasting, seasonal climate prediction, and our understanding of the physical, chemical and biological processes that occur within the soil.Recent advances in remote sensing have shown that microwave radiometry is a suitable approach to retrieve soil moisture.However, the quantitative aspects of remotely sensed soil moisture observations are not well-known, and validation of remotely sensed measurements is an important challenge.In this book, we described efforts made at Iowa State University to establish the framework needed for the validation of remotely sensed soil moisture observations.In the process of developing this framework, we engineered new tools that can be used by the remote sensing community.Then we gave an example of how these tools could be used to quantitatively compare remote sensing observations with models.