Presents an overview of the characteristics of anxiety and anxiety disorders. In the first section, the authors describe the basic characteristics of anxiety and discuss several issues in distinguishing between anxiety as a normal response and anxiety as a disordered response. The second section presents a brief review of the DSM-IV classification scheme for anxiety disorders. These include panic disorder, panic disorder with agoraphobia, specific phobia, social phobia, generalized anxiety disorder, obsessive compulsive disorder, posttraumatic stress disorder, acute stress disorder, and anxiety disorder not otherwise specified. The final section addresses mental and physical substrate factors, triggering factors, and maintenance factors in anxiety. (PsycINFO Database Record (c) 2012 APA, all rights reserved). (chapter)