--- - |2 Abstract What leads some women to form romantic and sexual relationships with men, and other women to form intimate relationships with women? This article presents a new conceptual paradigm for understanding women's sexual orientation that is emerging from research in such diverse fields as social psychology, sex research, evolutionary psychology, attachment theory, and neuroscience. This approach acknowledges the potential plasticity of women's sexuality and the emphasis that women place on close relationships as a context for sexuality. Research also raises the possibility that for women the biological determinants of sexual desire, attraction, and attachment are not inherently linked to a partner's gender. This article begins with a brief survey of research on women's same‐sex romantic and sexual relationships not only in the United States today but also in other cultures and historical periods. These and other findings are used to critique prevailing conceptual models of women's sexual orientation. Finally, key elements in an alternative paradigm are described. - Personal Relationships, Page 1-19, October 2018.