Peggy T. Cohen-Kettenis, Ph.D., is Professor of gender development and psychopathology at the Department of Child and Adolescent Psychiatry, University Medical Center Utrecht. She was a pre- and postgraduate student in developmental and clinical psychology at the University of Utrecht, The Netherlands. She was trained to become a registered clinical psychologist and psychotherapist at the Utrecht Institute for Multidisciplinary Psychotherapy. After completing her Ph.D. thesis, she worked at the Department of Clinical Psychology of the Utrecht University. There, she conducted a study evaluating sex reassignment, promoted by the advice of a committee of the Health Council, the medical advisory board of the Ministry of Public Health. The outcome of this study would also be the groundwork for a new law allowing transsexuals to adjust their birth certificates. In 1987, she started the first outpatient clinic in Europe for children and adolescents with gender problems and intersex conditions. In September 2002, she will become Professor of Medical Psychology at the Free University Medical Center in Amsterdam. There, she will be the head of a gender clinic for children, adolescents, and adults. Her main areas of research are gender identity problems and gender-related psychopathology. Friedemann Pfafflin, M.D., Ph.D., is Professor of Psychotherapy and head of the Forensic Psychotherapy Unit at Ulm University, Germany. Trained as a psychiatrist at Hamburg University, he first engaged in transgender clinical work in the mid-1970s when he visited the Psychohormonal Research Unit and the Gender Identity Clinic at The Johns Hopkins University Clinic in Baltimore, Maryland. From 1978 to 1992, he worked at the Institute of Sex Research at Hamburg University, Germany, and continued the work with transsexuals after moving to Ulm University in 1992. His main areas of research are transsexualism, transgenderism, psychotherapy process research, forensic psychiatry and psychotherapy, and history of psychiatry. From 1995 to 1997, he was President of the Harry Benjamin International Gender Dysphoria Association, Inc. Together with Eli Coleman, he founded The International Journal of Transgenderism in 1997.