Thomas A. Widiger, PhD , is the T. Marshall Hahn Professor of Psychology at the University of Kentucky, Lexington. He received his PhD from Miami University, Miami, Ohio, and completed his internship at Cornell University Medical Center, Westchester, New York. He is currently associate editor of the Journal of Personality Disorders, the Annual Review of Clinical Psychology, the Journal of Personality Assessment, and the Journal of Abnormal Psychology . He was the research coordinator for the fourth edition of the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) , a member of the DSM-IV Personality Disorders Work Group, and a cochair of the 2004 American Psychiatric Association DSM-5 Research Planning Conference, "Dimensional Models of Personality Disorder." His primary interest has been the integration of the American Psychiatric Association's personality disorder nomenclature with the dimensional classification of personality structure, particularly as the latter is conceptualized within the five-factor model. He also conducts research and writes papers concerning diagnosis, classification, the philosophy of science, personality disorders and personality disorder assessment, structured interviews and self-report inventories, gender bias, and clinical utility. He has authored of coauthored approximately 400 articles and chapters. In 2009, he received the Distinguished Scientist Award from the Society for a Science of Clinical Psychology.

Paul T. Costa Jr., PhD , is adjunct professor of medical psychology at the Duke University School of Medicine, Durham, North Carolina, and holds a joint appointment as professor in the Departments of Psychiatry and Behavioral Sciences and in the Department of Mental Health at the Johns Hopkins University Bloomberg School of Public Health in Baltimore, Maryland. Until 2009, he was chief of the Laboratory of Personality and Cognition, National Institute on Aging, Biomedical Research Center, in Baltimore, Maryland. Dr. Costa received his doctorate from the University of Chicago and taught at Harvard University and the University of Massachusetts at Boston before moving to Baltimore in 1978. His enduring interests are in the structure and measurement of personality and in life-span development. His other research interests include health psychology, personality disorders, and the neurobiology and molecular genetics of personality. With his long-term collaborator, Robert McCrae, Dr. Costa developed the Neuroticism-Extroversion-Openness (NEO) personalty inventories, including the NEO PI-3, the NEO PI-R, and the NEO-FFI, which are designed to operationalize the five-factor model (FFM). Not only has he been a leading contributor to the development of the FFM, but with Dr. McCrae he continues to develop the FFM. He has authored and coauthored approximately 400 papers and chapters. He is past president of several national and international personality organizations and the recipient of several awards, including the Distinguished Contribution Award from APA's Division 20 (Adult Development and Aging) and the Jack Block Award from the Society for Personality and Social Psychology.