Evidence for the importance of the serotonin system in anxiety disorders has increased substantially in recent years. Although preclinical research has provided an important source of hypotheses, clinical work on the value of selective serotonin reuptake inhibitors (SSRIs) in these conditions has been particularly persuasive. In this paper, a number of models of serotonin in the anxiety disorders are reviewed, and the clinical advantages of the SSRIs in anxiety disorders are emphasized. Models of serotonin in anxiety disorders include: 1) a 'see-saw model'; 2) an 'amygdala model'; and 3) a 'basal ganglia model'. While any simplistic schema in this complex area must fail, these various models have some heuristic value for the clinician. From a clinical perspective, the availability of the SSRIs has proved a significant step forward in the treatment of the anxiety disorders such as panic disorder, obsessive-compulsive disorder, post-traumatic stress disorder, and social anxiety disorder (social phobia); certainly these agents offer several advantages over previously existing pharmacotherapeutic alternatives such as the benzodiazepines and tricyclic antidepressants.