Written by a biopsychologist, this book describes and explains transsexualism and transgenderism (TSTG) from a scientific vantage point. Why does a male violate cultural gender rules and dress and act as a woman? Why does a female violate cultural rules to dress and act as a man? Why do some males and females undergo radical medical procedures in order to permanently change their bodies so that they are closer, respectively, to female and male bodies? In this book, a Princeton University-trained physiological psychologist explores dozens of theories about what may spur transsexual and transgender (TSTG) thinking, exposes the myths of fetishism, homosexuality, prenatal hormones, or child rearing as causes, and explains the two causes that are supported by current science. Covering a breadth of topics that include neuroanatomy, choice, psychodynamics, and transsexual transition, author Thomas E. Bevan, PhD, synthesizes the pertinent research regarding transsexualism and transgenderism across 22 scientific disciplines. The book covers various gender systems from antiquity to historical and contemporary cultures that support the biological basis of transsexualism and transgenderism, addresses human development from the time prior to conception through adulthood and potential transsexual transition, and corrects common myths and assumptions about TSTG individuals, such as that crossdressing is basically motivated by a desire for sexual arousal. The book also includes sections that cite definitions of key terms and identify related reading, organizations for support, and current TSTG events worldwide.