This lecture course explores the scientific literature underlying the concept that female/male, gay/straight, and transgendered behaviours are based on brain differences. Original scientific papers will be read in close detail for design and interpretation of the experiments. The goal is to gain an understanding of the science and psychology underlying sex/gender, popular conceptions of sex, and the sexual brain. Topics include: the making of sex, hormone action, brain-based sexual behaviours, sex and cognition, and sex and sexuality/gender identification.