This chapter summarizes the literature on assessment, maintenance, treatment,and mechanisms of change in treatment of patients with panic disorder with or without agoraphobia.Relevant theoretical contributions which are discussed may help to understand thegenesis and maintenance factors of panic disorder and agoraphobia. Further, we provide anoverview of empirically supported treatment approaches for these disorders and discuss themechanisms of change involved in these treatments Knowledge of the burgeoning literaturein this area is relevant for the development of basic and expert clinical competencies in panicdisorder/agoraphobia. It is argued that the clinician should first be familiar with the diagnosticcriteria for panic disorder and for agoraphobia. Knowledge of structured clinical interviewsis needed to be able to formalize the diagnosis. In addition, knowledge of self-reportmeasures, behavioral assessment, and self-monitoring is needed to assess the quality andseverity of panic disorder and agoraphobia and to evaluate progress of treatment. Further,basic competencies also require knowledge on which factors are involved in the maintenanceof these disorders. In addition, basic clinical competencies should entail knowledge aboutpsycho-education, and evidence-based protocols for conducting interoceptive exposure andexposure in vivo outside the therapist office. Expert clinical competencies may entail advancedunderstanding and skills of applying psychological and pharmacological proceduresto augment exposure therapy, skills in enactment of cognitive therapy and couple therapy,knowledge and skills to deal with panic disorder and agoraphobia in cases with comorbiddisorders (e.g. substance abuse/dependence, and depression) as well sensitivity to anxietyrelated cultural factors.