The Forest Inventory and Analysis (FIA) program of the USDA Forest Service conducts a national inventory of forests of the United States. A subset of FIA permanent inventory plots are sampled every year for numerous indicators of forest health ranging from soils to understory vegetation. Down woody material (DWM) is an FIA indicator that provides estimates of forest structural diversity, forest area fuel loadings, and national carbon sources. DWM comprises fine woody debris, coarse woody debris, slash piles, duff, litter, and shrub/herbs. Components of DWM are sampled using the line-intersect method and fixed-radius sampling. DWM data analyses serve as integral parts of national inventory reporting requirements, regional/national forest health reports, wildlife habitat assessments, and fuel loading maps. The DWM inventory began in 2001 and is currently implemented in 38 States. The goal of this document is to provide the rationale and context for a national inventory of down woody material; document the various woody material components sampled by the DWM indicator, the sampling protocol used to measure the DWM components, and estimation procedures; and provide guidance on managing and processing DWM data and incorporating that data into pertinent inventory analyses and research projects.