The description of the human genome structure only 20 years ago has accelerated our ability to understand the genetic components of human sexuality and to assess their interaction with hormones in the establishment of phenotypic sex. The view that the world’s population can be separated into a clearly defined dyadic unit of male and female is defunct; not only clinical observations but molecular biology has established that sexual identity is on a continuum, with an enormous potential for variance. The search for the specific biological factors that determine a sense of being male or female, the anatomy of the reproductive system, and whether sexual inclination is homosexual or heterosexual is accelerating, but the data are still far from complete. The interest of the lay public in neutralizing the prejudice and distaste for variations in human sexual identity and behaviour is intense. It is our responsibility to continue to delineate the molecular biology of what makes us male or female and to explore the many, heretofore largely concealed and often subtle variations that place an individual on a continuum. Those who do not fit into the dyadic view of human sex as either male or female can no longer be regarded as an anomaly to be rejected, condemned, and, if possible, “corrected,” either psychologically or anatomically.