The use of alcohol, tobacco, pharmaceuticals and illicit drugs involves a wide variety of adverse health and social consequences. There is a strong need for improved estimates of the economic costs of substance abuse. This document presents a general framework for the development of cost estimates. Studies of the economic costs of substance abuse are described as a type of cost-of-illness study in which the impact of substance abuse on the material welfare of a society is estimated by examining the social costs of treatment, prevention, research, law enforcement and lost productivity plus some measure of the quality of life years lost, relative to a counterfactual scenario in which there is no substance abuse.