This chapter focuses on the substance abuse and chronic pain. Substance abuse is a significant problem among people with chronic pain. Individuals with substance use disorder (SUD) are at a higher risk of comorbid chronic pain than those without SUD and are more likely to be diagnosed with a comorbid mental health problem. Unfortunately, chronic pain patients with SUD are likely to respond poorly to treatment and both problems are likely to exacerbate one another, leading to increased symptom severity. Factors underlying substance use disorder and chronic pain comorbidity are complex, so assessment and intervention should tap multiple dimensions including physical, emotional, functional, behavioral, and environmental factors. Chronic pain patients should be regularly screened for SUD, especially when treated with opioid medications.