The present state of knowledge on the genetics of anxiety disorders, in particular panic disorder, comprising clinical and molecular genetic studies, interaction analyses, as well as meta-analyses of single association studies will be presented in detail. A particular focus will be on the most robust findings in panic disorder to date in the serotonergic, noradrenergic, and dopaminergic system, such as the catechol-O-methyltransferase (COMT) gene. Additionally, findings on the adenosine receptor 2A (A2A) gene, which has been reported to be associated with panic disorder and also with anxiety levels after caffeine administration in a gene--environment interactional model, will be discussed. Furthermore, the first imaging genetic findings in panic disorder, social phobia, and anxiety-related traits using fMRI and PET techniques in combination with molecular genetic association analyses are reviewed, taking into account the present intermediate phenotype discussion in the investigation of complex genetic disorders. Finally, the first exemplary pharmacogenetic studies in panic disorder and generalized social phobia will be presented. The pathomechanism of anxiety disorders and in particular panic disorder is considered to be multifactorial with converging evidence for a pivotal role of genetic factors in particular, which will be presented in detail in this chapter.