An overview of the state of the art of research on the treatment services of the therapeutic community for drug addicts in Europe is presented. This research tradition has largely been fragmented and local in its implementation. There has been a scientific gap concerning evaluation research and the treatment services offered by the therapeutic community. The American research antecedents to the European tradition are reviewed. The essential European groups, research designs and results are presented for each country with something greater than an ad hoc study experience. The strengths and weaknesses of the research designs, results and organizations are critically assessed. Recommendations for future research are presented and referenced to specific recommendations for therapeutic community research coming out of an American National Institute on Drug Abuse Technical Review. Among the conclusions of the overview is the need for more qualitative phenomenological research to complement the existing quantitative approach.