The Resources Planning Act (RPA) Assessment uses a combination of land use and land cover data to evaluate trends in the United States land base and project future changes. This publication describes how the RPA Assessment uses the National Resources Inventory, National Land Cover Database, and Forest Inventory and Analysis to support analyses of forest trends. The authors compare and contrast differences in definitions and approaches of these three major data sources and document the recent status and trends of land use and land cover area according to these sources. While the general definitions of land uses and land covers are superficially similar among these sources, understanding the conceptual and technical differences between them is necessary to evaluate and compare trends in the U.S. land base. Some differences can be rationalized based on the sensitivity of the different databases to the underlying drivers of landscape change over time. However, the major difference is the perception of the land base in terms of its intended human use versus its current biophysical cover. The RPA Assessment will continue to use both land use and land cover data separately and in combination because each source offers both unique and complementary perspectives on land base trends.