Opioid abuse is a complex problem, which not only impacts on the affected individuals' physical and psychological health, but also threatens public security and the productivity of the society. Further, through needle sharing and sexual contacts, injecting drug users (IDUs) have become laden with HIV and HIV related health problems, representing a serious public health threat all over the world. In Taiwan, since the identification of the first HIV-infected IDU in 1987, the incident cases have continued to increase, reaching a height of 2,461 in 2005. In order to contain the epidemics of HIV among IDUs, and to prevent its spread to the population in general, the Center for Disease Control (CDC) collaborated with the Department of Justice to initiate and implement a number of harm reduction programs in 2005. The fact that opioid addiction is officially treated as a health rather than a legal issue itself represents a remarkable milestone in Taiwan. Among these harm reduction programs, including needle and syringe exchange for IDUs as well as substitution treatment approaches for opioid dependence, methadone maintenance treatment (MMT) perhaps represents the most most important and most crucial component. Remarkably, in a relatively short time span, more than 60 MMT programs were established, which enrolled more than 15,000 heroin addicts. This notwithstanding, the overall and differential effectiveness of these MMT service delivery systems, as well as the characteristics of these programs and the patients that might contribute toward treatment response or failure remain largely unknown. Such knowledge base is crucial for establishing standardized and feasible outcome evaluation processes for opioid addicts receiving MMT programs, as well as for the further improvement of the efficacy and effectiveness of these programs, in Taiwan.