The identification of the disease of addiction is important to safe and effective clinical management of pain in persons with addictive disorders. The disease of addiction affects approximately 10% of the general population, and its prevalence may be higher in subpopulations of patients with pain. The presence of active addiction may facilitate the experience of pain. Both active and recovering addiction may complicate the use of medications, such as opioids, important to the management of pain. There is, further, persistent misunderstanding among health care providers, regulators, and the general population regarding the nature and manifestations of addiction that may result in undertreatment of pain and stigmatization of patients using opioids for pain control. The author seeks to clarify understanding of addiction, to underscore the importance of identifying addiction in the context of pain treatment, and to provide a rational approach to assessment for addiction in patients with pain. Current scientific understanding of addiction as a chronic illness is briefly reviewed. Recent definitions related to addiction are presented. The impact of addictive disorders on pain and pain treatment are explored. The roles of medical interview, physical examination, laboratory studies, and standard addiction screening tools in assessing for addiction are outlined. Differential considerations in distinguishing therapeutic use of opioids for analgesia from addictive or other nontherapeutic use of opioids are discussed. In summary, the article provides salient background and a detailed approach to assessment for addictive disorders in the context of pain treatment.