Since 1939, the U.S. government, using the National Defense Stockpile (NDS), has been stockpiling critical strategic materials for national defense. The economic and national security environments, however, have changed significantly from the time the NDS was created. Current threats are more varied, production and processing of key materials is more globally dispersed, the global competition for raw materials is increasing, the U.S. military is more dependent on civilian industry, and industry depends far more on just-in-time inventory control. To help determine the significance of these changes for the strategic materials stockpile, the Department of Defense asked the NRC to assess the continuing need for and value of the NDS. This report begins with the historical context of the NDS. It then presents a discussion of raw-materials and minerals supply, an examination of changing defense planning and materials needs, an analysis of modern tools used to manage materials supply chains, and an assessment of current operational practices of the NDS.