Queer theory is a deconstructionist theory about individuals' sex and gender in Queer studies. It proposes the theory that one's sexual identity is partly or wholly socially constructed, and therefore individuals cannot really be described using broad terms like "homosexual" or "woman." It challenges the common practice of compartmentalizing the description of a person to fit into one particular category.

In particular, it rejects the creation of an artificial and socially assigned identity and membership in a group-entity to which all who share some habit or lifestyle defined by standards set by The Other (those who are not in fact participating) are relegated. It considers individuals to be just that, individuals, and requires building up categories and groups by voluntary and especially aesthetic associations.

The primary influence in the development of Queer theory was Michel Foucault; later theorists include Judith Butler and Eve Kosofsky Sedgwick. Earlier historical influences include Jacques Lacan, Louis Althusser, and Jacques Derrida.

Like those in some branches of feminism, many scholars in Queer theory view prostitition, pornography and BDSM as legitimate and valuable expressions of human sexuality. For example, Patrick Califia in Feminism and Sadomasochism (ISBN 1573440965) writes about how sadomasochism encourages fluidity and questions the naturalness of binary dichotomies in society: "The dynamic between a top and a bottom is quite different from the dynamic between men and women, blacks and whites, or upper- and working- class people. That system is unjust because it assigns privileges based on race, gender, and social class. During a S/M encounter, roles are acquired and used in very different ways… if you don’t like being a top or bottom, you switch your keys. Try doing that to your biological sex or your race or your socioeconomic status."

This places them in conflict with branches of feminism that view them as mechanisms for the oppression of women.

Critics hold that a strict body-based version of Queer theory is totally baseless from a scientific point of view. They point to a vast and growing body of physiological, genetic and sociological evidence that most scientists accept as proving that sexual orientation is more than a social construct. In this view, sexuality is innate and exists independently of whatever any given society happens to teach on this subject. Many scientists hold that deconstructionist claims about science (not only on this topic) are pseudoscience.

However, it is not easy to claim that all individuals fall into the category of "male" or "female", based on biological characteristics. Chromosomes can exist in atypical pairs leading to Klinefelter's syndrome and it becomes difficult to categorize these pairs as being "male" or "female". Intersexed individuals also challenge the notion of genital classification of people into "male" and "female" characteristics.

The biological aspects are not as relevant to those who view the process of construction as taking place within natural language and categories it forms by frequent reinforcement in minds - pronouns for instance that make gender or formality distinctions. In Jacques Lacan's model of psychology, the mirror stage (around age 3 where a child sees themselves in a mirror and believes that image to be their "self") and development of language occur at approximately the same time. Indeed, it may be language that constructs the entire idea of self, and gender/sex distinctions as well. Ferdinand de Saussure's ideas of sign-signifier relationships in language are also used to demonstrate this concept as well. It is seen that although some biological truths may exist, our knowledge and conceptualization of them is always mediated by language and culture.

A middle ground between a body-based and language-based view is to hold that society constructs expectations and identities around innate characteristics of sexual life; for example, to acknowledge the fact of sexual orientation and to point out and deconstruct the social constructs surrounding that fact. Queer theory contextualizes the biological notions of sexual orientation and gender within a historical and cultural framework.

See Queer, gender role, gender studies, post-structuralism, critical theory