A gender bender is a person who dresses up and presents themselves in a way that defies societal expectations of their gender, especially as the opposite sex. Bending expected gender roles may also be called a genderfuck.

The concept of gender bending may have political origins, stemming from movements in the 1960s and 1970s, a guiding principle of which is the idea that the personal is political. Some individuals may choose to engage in gender bending as a form of self-expression or to challenge societal norms; in his 1974 article, Genderfuck and Its Delights, Christopher Lonc explained his motivation for performing genderfuck: "I want to criticize and poke fun at the roles of women and of men too. I want to try [to] show how not-normal I can be. I want to ridicule and destroy the whole cosmology of restrictive sex roles and sexual identification."

The term genderfuck has long been part of the gay vernacular, and started to appear in written documents in the 1970s. Sheidlower cites the definition of the term gender fuck in L Humphreys' 1972 work Out of the Closets: Sociology of Homosexual Liberation as "a form of extended guerilla theatre". Also quoted is the August 1972 issue of Rolling Stone magazine, in reference to the glam rock style: "The new 'macho' transvestism, called vulgarly 'gender-fuck', a curious satire of female impersonation – dresses, pumps, full make-up and beards – is represented by, among others, three men in WAC uniforms and big moustaches".

Gender bending is commonly used as a rebellion against socially constructed expectations of gender and gender roles, which can vary widely between cultures, though commonly include some variation of the gender binary – the idea that only two genders exist: men and women. In many cultures, it is only acceptable for an individual to embody one of these two gender roles, which often mimic the social expectations of the sexual categories of "male" and "female". Within this cultural expectation, people designated as male are expected to be masculine, while those designated female are expected to be feminine. The belief in and subscription to polar gender roles is known as "gender binarism".

In many cultures, for a person to be seen as belonging to a particular gender category, the individual must not only have a particular anatomical (including genital) makeup, but must conform to that culture's ideas of appropriate sex role stereotypes. These roles are highly influenced by culture and peers. This sex role stereotype includes sexual orientation. To this end, those who go against expected conduct, for example gays and lesbians, may be seen as "less than" or "other".

In Western cultures, gender roles have changed over many centuries, though mainstream Western culture still tends to expect stereotypical "feminine" behaviors from females, and "masculine" sex role stereotypes from males. A study by Princeton University outlined these common, prescriptive gender stereotypes:

In Christian and Jewish cultures, gender roles and gender presentation have formed part of scriptural texts and religious teachings for thousands of years: "The woman shall not wear that which pertaineth unto a man, neither shall a man put on a woman's garment; for all that do so are abomination unto the Lord thy God" (KJV, Deut. 22:5). Crossing these lines has been interpreted by some Christians as a moral transgression. Jewish law, or halacha, recognizes ambiguous and non-conforming genders in addition to male and female. Rabbinical literature recognizes six different genders, defined according to the development and presentation of primary and secondary sex characteristics at birth and later in life. Jewish literature describes what today would be referred to as intersex such as the concept of a Tumtum being a person of ambiguous gender and/or sex as is the concept of the androgynos, being a person characterized with elements of both sexes. One aspect of gender and Jewish studies is considering how the ambiguity recognized in Rabbinical literature has been erased and constructed into a binary and how this translates into Jewish practices.

Other cultures – often indigenous peoples, or subcultures that exist within Western cultures – may conceptualize gender as having more than two options, and even see their people as potentially fulfilling more than one gender role. Some indigenous peoples of North America have historically had more than two gender roles as part of their social structure, while others, who may or may not have embraced this diversity historically, may accept modern two spirit people as part of their communities now. Other cultures may see people as being capable of embodying more than one gender role at different times, or of being "in the middle", "embracing both male and female spirit". One such example is the Bugis people of South Sulawesi, Indonesia. People of the Bugis society have a total of five genders. These genders include what would traditionally be seen as cisgender man and woman, as well as transgender men and women, and the androgynous Bissu shamans.