Technical Abstract: Surface soil moisture (ms) is the average moisture (cm3 cm-3) in the top few centimeters of soil over a heterogeneous volume. Such information at spatial resolutions of 10 to 100 m and spatial coverage ranging from 1,000 to 25,000 km2 would be useful for many watershed management applications. A feasible way to determine distributed surface soil moisture at this resolution and coverage is through the use of satellite-based sensors, particularly those measuring microwave backscatter. This review summarizes the state of the science using current satellite-based sensors to determine regional surface soil moisture distribution. The basic conclusion of this review is that currently orbiting sensors can provide ms information with known accuracy at the watershed scale. The priority areas for future research should include active and passive microwave data fusion, determination of soil moisture in densely vegetated sites, and image-based approaches for mapping surface roughness. However, to realize a truly operational system for watershed management, it will be necessary to continue sensor development, improve image availability and timely delivery, and reduce image cost.