This guideline on opioid use disorder (OUD) in older adults (age ≥ 65) is one in a series of four that also includes alcohol, cannabis, and benzodiazepines. Primarily, these guidelines are targeted to primary care clinicians and specialists serving older adults. In addition, these guidelines are meant to inform patients, caregivers, and care facility administrators. These guidelines are not intended to provide a comprehensive guide on the use of opioids either by medical prescription or recreationally. Rather, the goal of this document is to provide useful guidance for clinicians on preventing the development of OUD and optimally assessing and treating older individuals who have developed such a disorder.