Women are objectified and sexualized by the media and the economy, so that they live in a culture of sex. Lesbians are excluded from the mainstream sexual and appearance norms for women, yet are affected by these norms, including the association of sex and violence against women. The word sexuality has been used to connote both sexual orientation and sexual activity, and it is argued that this dual meaning illustrates the dominance of patriarchal definitions of women's sexuality. This article discusses methodologic issues in understanding who is a lesbian and presents various models or dimensions for understanding who is included in research about lesbians. It asks the question “What is sex?” and reviews the implications of this question for lesbian sexual activity. This question has implications for a collorary question: “What is a lesbian relationship?”, and the article discusses the implications of this question on various forms of sexual and nonsexual relationships among lesbians.