Several countries are experiencing public health crises as a result of opioid addiction. Fatal overdoses have reached record highs in many regions and Hepatitis C virus is the norm among people who inject drugs in several countries. Thus, providing for the global availability of medication-assisted treatment (MAT) for opioid addiction is more important than ever. In this article, we introduce readers to the collection of papers that appear in this special issue on MAT for opioid addiction. We describe the articles and commentaries thematically to include topics that address 1) the contemporary history of methadone maintenance, 2) the provision of and access and barriers to MAT, 3) compliance and outcomes of MAT, 4) health issues among MAT patients, 5) race, ethnicity, and social class backgrounds of MAT patients, 6) criminalization and stigma, and 7) challenges associated with the expansion of MAT.