This text provides in-depth coverage of the diagnostic and conceptual issues related to classification in the context of anxiety disorders. Diagnosis of anxiety related problems serves as a useful model for considering classification. Several groups of investigators have begun to consider revisions to the classification of anxiety disorders. There are numerous empirical issues ranging from neurochemical bases of specific fears (i.e., social anxiety) to cognitive biases (i.e., memory and encoding) to fear circuitry (i.e., interactions of brain abnormalities and genetic dispositions) that are evident across anxiety problems. These empirical developments set the stage for a closer examination of how these disorders are classified. This empirically based book therefore covers the full spectrum of empirical approaches used in the study, diagnosis, and classification of anxiety problems.