The brains of heterosexual males and heterosexual females are different. Moreover, the brains of gay men are similar to heterosexual females whereas the brains of lesbians are similar to heterosexual males. Neuroscience research supporting these postulates is reviewed. The gestational processes that might explain the differences in brain structure and function corresponding with gender are reviewed. Following a discussion of the physiological bases for sexual orientation, a discussion of the physiological bases for the expression of gender related traits and a discussion of factors contributing to sexual identity are provided. Throughout the article, alternative ways to think about gender are suggested. The importance of integrating the information presented in this article into the curriculum of Social Work Education is explained.