The rationale for the National Institute on Alcohol Abuse and Alcoholism's demonstration research program on the topic is that drug abusers who are homeless represent a special population who have traditionally not been well served by public treatment programs and that these people have special needs that must be recognized in a drug treatment program. However, the prevalence of drug use among the homeless is unknown. One recent meta-analysis revealed that approximately half of the homeless could be classified as having a drug abuse disorder, although current prevalence rates were much lower. One population important for service planning consists of homeless black men and women in large cities. Crack cocaine seems to be particularly prevalent among this group. Research on the causes of homelessness suggests the critical importance of structural factors that include poverty; disabilities have a role for some individuals. The subsequent articles aim to aid understanding of the clients and service systems designed to help people who are both homeless and drug abusers. Notes and 44 references