The challenges of retaining populations in treatment services who are hard-to-reach and suffer from multiple health issues continue to be studied. Informing health professionals about the latest knowledge in this regard is vital. This book can be used by professionals and non-professionals who are working with alcohol and drug addicted individuals and those who are also HIV-infected. In addition, it is a great resource for academic faculty and students who are interested in learning the theories and strategies related to Motivational Interviewing and the Transtheoretical Model of Stages of Change. This work describes the broad aspects of alcohol and drug addiction as well as HIV/AIDS, along with their treatments. A research study was conducted using Motivational Interviewing sessions to measure the impact of retaining clients in treatment services who were alcohol and drug addicted and who may have also been HIV-infected. This book provides helpful strategies and recommendations when working with clients who are difficult to reach and are more likely to terminate treatment services.