Anxiety disorders commonly co-occur with substance use disorders both in the general population and in treatment-seeking samples. This co-occurrence is associated with greater symptom severity, higher levels of disability, and poorer course of illness relative to either disorder alone. Little research has been conducted, however, on the treatment of these co-occurring disorders. This gap may not only leave anxiety untreated or undertreated but also increase the risk for relapse and poor substance use outcomes. The aim of this article is to review the current state of the literature on treating co-occurring anxiety and substance use disorders. In addition to presenting a brief overview of the epidemiology of this co-occurrence, the article discusses the challenges in assessing anxiety in the context of a substance use disorder, the evidence for various treatment approaches, and recent advances and future directions in this understudied area. Also highlighted is the need for future research to identify optimal behavioral and pharmacologic treatments for co-occurring anxiety and substance use disorders.