Data from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor has been used since 2001 by NASA scientists to produce eight-day estimates of Gross Primary Production (GPP) and annual estimates of Net Primary Production (NPP) for each 1-km2 cell of the Earth's terrestrial surface. These data have great potential utility for monitoring the NPP component of the global carbon cycle and for assessing regional responses to climate variation, including effects on agriculture and forestry. The assessment and validation of these products will require a network of sites focused on validation, and the goal of the GTOS NPP Demonstration Project is to coordinate that validation activity.