Opioid use disorder is a chronic relapsing medical condition characterized by a compulsive pattern of opioid seeking and use, despite harmful consequences, and defined by specific diagnostic criteria. As a research concept, it encompasses the systematic investigation of the complex interplay of genetic, neurobiological, and psychosocial factors underlying its etiology, development, and maintenance. Research in this field examines its epidemiology, clinical manifestations, neurobiological basis, and the efficacy of various pharmacological and behavioral interventions, reflecting its significance as a major global public health challenge requiring multidisciplinary scientific inquiry.