Anxiety disorders commonly occur among those with substance use disorders. This article reviews the literature describing the prevalence and patterns of this comorbidity in epidemiological and clinical samples and theoretical models explaining this comorbidity, and reviews the effects of anxiety disorders on substance use outcomes and data from clinical trials that target comorbid anxiety disorders to examine the effects of treating anxiety disorders on substance use outcomes. Next, this review outlines evidence-based pharmacological and psychological treatments for anxiety disorders and provides treatment recommendations for those treating this comorbid population. Finally, a discussion of treatment-delivery issues is presented to address the important issues that arise when treating anxiety disorders in typical addictions-treatment settings.