Given the relative lack of research on the comorbidity of anxiety disorders (ADs) and conduct problems (oppositional defiant disorder, conduct disorder) in youth, we examine this comorbidity from both basic and applied perspectives. First, we review the concept of comorbidity and provide a framework for understanding issues pertaining to comorbidity. Second, we examine the comorbidity of ADs and conduct problems in both epidemiological and clinical studies. Third, we explore the artifactual and substantive reasons for the comorbidity of these disorders. Finally, we discuss the implications of comorbidity for assessment and treatment and provide recommendations for future directions in clinical research and practice.