Acknowledging that the traditional understanding of sex and gender has been binary (i.e. female and male as distinct and separate expressions of biology and psychology), the author of this entry encourages readers to rethink these concepts to understand a more complex continuum of gender. The historical binary approach to these concepts served as an affirmation that not only are women and men different, but that the differences that exist are essential, innate, and unchangeable. This limited approach to understanding sex and gender further focuses on the differences between females and males, or women and men, equating to ingroup bias and the prejudiced superiority of one sex over the other. More recently, researchers have demonstrated that whereas sex and gender may seem like simple and biological classifications, the reality is that the experiences of sex and gender are quite complex. Additionally, research suggests that although the concepts are intertwined, they are separately experienced and expressed.