The SUPPORT for Patients and Communities Act (P.L. 115-271) requires MACPAC to send a letter to the Secretary of the U.S. Department of Health and Human Services defining the eligibility groups that should be included in the Department’s forthcoming data book on the prevalence of substance use disorders in the Medicaid population. In this letter, the Commission recommends eight major eligibility groups to include in the report, and suggests several special populations that are particularly affected by the opioid epidemic, if data are available.