This chapter explores the effects of both licit and illicit substances of abuse on sleep and the reciprocal relationships among them. Early detection of sleep disturbance in children at high risk for developing a substance use disorder may help in the effort to prevent the onset of substance use disorders. Insomnia is an extremely common sleep complaint in patients who are actively drinking alcohol as well as in patients who have recently stopped drinking. When approaching patients with both substance use disorders and insomnia, clinicians should assume that substances may be only one of many causes of their sleep disturbance. Sleep disturbance that remits within approximately four weeks of abstinence may be regarded as substance-induced and not requiring further treatment. Behavioral therapy for insomnia in patients with substance use disorders also shows promise and should be considered.