Generalized anxiety disorder (GAD) is one of the least studied and least clearly conceptualized of the anxiety disorders. The present article reviews the information which currently exists on the nature and treatment of GAD. An attempt is made to integrate clinical aspects with theoretical conceptualizations of the disorder. It is found that while the reliability of the disorder appears to be moderately good, further improvement could be made by more operationalized criteria. Further, a similarity between GAD and high trait anxiety is noted such that at a theoretical level, GAD could be conceptualized as the "basic" anxiety disorder. This point suggests that increased research into GAD may be of benefit to all of the anxiety disorders. In addition, etiological factors have received little attention, although there has been a recent surge of research interest into potential maintaining factors. A model of the maintenance of GAD from an information processing perspective is described. Finally, a number of treatment studies are reviewed indicating considerable promise but, currently, a number of limitations. It is hoped that such a review will not only highlight the importance of further research into GAD, but may also help to clarify some of the issues which require investigation.