The authors present an overview of the work in progress on DSM-IV. After a brief historical review, they discuss the principles and multiple purposes of the DSM-IV effort and outline the three stages of its empirical documentation: systematic literature reviews, analysis of unpublished data, and field trials. Next, they discuss several of the basic conceptual issues that are implicit in revising a nomenclature. These include the definition of mental disorder, the balance between multiple diagnosis and differential diagnosis, the use of categorical and dimensional models of classification, and issues involved in the construction of criteria. Finally, they summarize the most important specific questions being reviewed by each of the DSM-IV work groups.