Opioid use disorder (OUD) is characterized by a compulsive pattern of opioid use leading to dependence, tolerance, and an inability to control use despite health consequences and impairment. The impact of OUD is widespread, impacting social, economic, health, and legal domains. The diagnosis is primarily clinical and is based on criteria outlined in the DSM-5, including patterns of opioid misuse and behavioral symptoms. The clinical features include those of opioid intoxication, withdrawal, and chronic manifestations of opioid use. Addressing this disorder requires a multifaceted approach including medication-assisted-treatment (MAT), psychosocial interventions, and harm reduction techniques.