The Diagnostic and Statistical Manual of Mental Disorders (DSM) was created in 1952 by the American Psychiatric Association so that mental health professionals in the United States would have a common language to use when diagnosing individuals with mental disorders. Since the initial publication of the DSM, there have been five subsequent editions of this manual published (including the DSM-III-R). This review discusses the structural changes in the six editions and the research that influenced those changes. Research is classified into three domains: (a) issues related to the DSMs as measurement systems, (b) studies of clinicians and how clinicians form diagnoses, and (c) taxonomic issues involving the philosophy of science and metatheoretical ideas about how classification systems function. The review ends with recommendations about future efforts to revise the DSMs.