This paper reviews the world literature on methadone. Methadone has been used in hundreds of thousands of patients, in disparate social, economic, cultural, and geographic situations; it has been evaluated in scores of studies. The large majority of evaluations demonstrate that opioid use, criminality, and general health status are affected positively in many addicts. Smaller gains in job and family functions are noted. Alcoholism and multiple drug use complicate treatment for some addicts. Despite the positive data, public opinion remains negative about this treatment. The use of methadone in withdrawal from opioid dependence and in pregnancy complicated by opioid dependence is discussed.