This notice of funding opportunity (NOFO) seeks to support studies that will inform safe and effective medication-assisted, psychosocial, and complementary interventions for people with co-occurring Opioid Use Disorder (OUD) and Alcohol Use Disorder (AUD). Alcohol increases lethal opioid overdose risk. As a result, treatment providers may under-prescribe or be reluctant to provide opioid agonist therapies (OATs) such as methadone and buprenorphine to people with OUD who also have AUD or misuse alcohol. There is also scant research on non-pharmacological therapies for people with OUD-AUD. Reciprocal relationships between opioid use and alcohol use has been observed for OUD-AUD patients such that reduced opioid intake may result in increased drinking which heightens opioid relapse and overdose risk and suggests an urgent need for targeted therapies in this population. Research projects dedicated to OUD treatment and prevention, while not excluding subjects who drink, seldom explicitly recruit subjects with AUD. The purpose of this NOFO is to support secondary analysis of data from relevant clinical projects and archives, and to support new hypothesis-clarifying studies to identify how people with OUD-AUD are being treated and associated treatment outcomes, identify challenges for treating people with OUD-AUD, and formulating best treatment practices for this population.