This version of Drug Availability Estimates in the United States (DAEUS) provides supply-based estimates for four major illegal drugs (cocaine, heroin, marijuana, and methamphetamine) in the United States. Availability measures are important to policy formation, execution, and monitoring. Reliable estimates have been difficult to develop because of the clandestine nature of drug production and trafficking. Nevertheless, the last decade has produced credible approaches, and, building on those emerging methodologies, an interagency team assembled by the Office of National Drug Control Policy issued a consensus statement identifying the best approaches for estimating the 2001 supply of drugs to the United States (Drug Availability Steering Committee, 2002). The methodology has since evolved, in part because the original methodology was inadequate, producing estimates that contradict other evidence about levels and trends in drug use in the United States.