Residential treatment services have been a core component of the alcohol and drug treatment system in the UK and internationally for a number of years, yet continue to provoke debate about their role and their effectiveness, particularly given concerns that they are expensive and too disruptive to the lives of people who are trying to reintegrate with their families, find employment and establish stable homes. What we set out to do in this review is to overview the evidence in two areas - first the overall evidence, largely from cohort studies, about whether residential treatment services are effective. Much of this work comes from (predominantly) drug treatment effectiveness studies. We then follow this up with a more detailed analysis of what the evidence base is for one particular kind of residential treatment - the Therapeutic Community. This review is important at this time when funding for alcohol and drug treatment is under great pressure. Service users, providers and commissioners all share a desire and need for a clear evidence base in order to allocate critical and limited resources effectively and efficiently. This review is intended to increase stakeholders' and interested persons' knowledge and understanding of the operation of this sector of alcohol and drug treatment services and guide decisions towards enhancing and improving outcomes