The American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders provides the authoritative list of what are considered to be mental disorders. This list has a tremendous impact on research, funding, and treatment, as well as a variety of civil and forensic decisions. The development of this diagnostic manual is an enormous responsibility. Provided herein are lessons learned during the course of the development of the fourth edition. Noted in particular is the importance of obtaining and publishing critical reviews, restraining the unbridled creativity of experts, conducting field trials that address key issues and concerns, and conducting forthright risk-benefit analyses. It is suggested that future editions of the diagnostic manual be developed under the auspices of the Institute of Medicine. The goal would be broad representation, an evidence-based approach, disinterested recommendations, and a careful attention to the risks and benefits of each suggestion for change to the individual patient, to public policy, and to forensic applications.