The toolkit is a practical and accessible guide for implementing data collection in core areas. The modules are designed to be the basic guide for the development of specific activities. The principles of data collection presented are the product of a consensus among an international panel of experts and have been endorsed by state members of the United Nations. Although based on working models that have proven their effectiveness, the user is guided through the process of adapting the general principles and models to specific contexts. The focus of prevalence estimation is to determine how many members of the population of a country are using drugs and whether this number is changing. Obtaining this data is useful in assessing the likely impact of drug abuse on society and the level of response required. The indirect estimation methods presented in this toolkit are most appropriate for estimating the number of chronic or problematic drug abusers such as street heroin addicts or drug injectors. This is because the estimation methods described often rely on data from organizations that customarily have contact with drug users who manifest drug-related problem behaviors serious enough to warrant police and/or treatment intervention or cause the death of the drug user. A chapter on drug-use prevalence assessment considers the importance of assessing harm, the role of general population surveys, other epidemiological methods, indirect methods of prevalence estimation, and national and local prevalence studies. A chapter on specific methods of prevalence estimation focuses on the use of multiplier-benchmark methods, capture-recapture methods, advanced modeling techniques, extrapolation from local to national prevalence estimates, and the accuracy of estimates of prevalence levels. The concluding chapter presents general and technical guidelines for producing research-based estimates. 12 tables, 11 case studies of prevalence estimates, and an appended list of general resources for prevalence studies