This chapter gives the overview of anxiety disorders. This chapter is divided into three parts following as general aspects of anxiety disorder, panic disorders, and generalized anxiety disorders. Anxiety disorders are the most prevalent mental disorders in the general population. Nearly 35 million peoples are affected in United States and more in other countries. The patient with anxiety or a panic state is a common problem in the emergency department worldwide. The modern classification of anxiety disorders is controversial, which is reflected in DSM-III. However, this controversy has been resolved up to some extent in ICD-10 and DSM-IV. Generalized anxiety disorder (GAD), one of the anxiety states described in DSM-III, was a relatively new diagnostic entity in DSM-III. It was conceptualized as a residual diagnostic category for those patients who did not meet the criteria for other diagnosis, but were characterized by apprehensive expectation or chronic worry focused on multiple life situations.