Gender expression (or gender presentation) is a person's behavior, mannerisms, interests, and appearance that are associated with gender in a particular cultural context, typically understood in terms of masculinity and femininity. Gender expression is an external display of one's gender identity, through aspects such as clothing, hairstyles, voice, makeup, body language, and behavior.

A person's gender expression may align with traditional gender roles or may be gender nonconforming, incorporating both masculine and feminine traits or neither. It may or may not reflect their gender identity or sex assigned at birth. Gender expression is influenced by sociocultural norms and is distinct from both gender identity and sexual orientation.

Although gender expression is often assumed to reflect a person's internal gender identity, the two are not always aligned. For example, some transgender people may adopt expressions that differ from their gender identity for reasons of safety or comfort. Gender expression also differs from sex assigned at birth and is independent of sexual orientation.

Expressions that diverge from conventional norms may be described as gender nonconforming. Common examples include men wearing makeup or dresses, and women with short hair or traditionally masculine attire. Some individuals adopt an androgynous or gender-neutral appearance, blending or rejecting traditional markers of masculinity and femininity.

Certain terms are used to describe gendered expression within specific subcultures. For instance, in queer women’s communities, "butch" and "femme" refer to more masculine or feminine styles respectively. In men and boys, atypically feminine expression is described as effeminate; atypically masculine expression in girls and women is described as tomboyish.

The term gender expression appears in legal contexts such as the Yogyakarta Principles and is recognized in the human rights laws of countries like Canada.

While gender expression does not necessarily connect to sexuality, individuals often are misinterpreted as more masculine if lesbian and more feminine if gay, regardless of the individual's gender expression. These beliefs can lead to people misinterpreting an individual's gender expression based on their sexuality. Studies on adolescents conducted show that gay and lesbian individuals who did not express themselves as their assigned gender were seen as less acceptable. Individuals who expressed themselves with their assigned gender typically faced less social harassment and discrimination. On the other hand, heterosexual males whose gender expression was more feminine than masculine were the most discriminated against.

The heterosexual matrix theory created by gender studies scholar Judith Butler says that people often assume someone's sexuality based on their visible gender and sex. It is one explanation why people tend to assume someone's gender expression based on their sex and sexuality. Some sexologists, especially earlier on in the 20th century, viewed being gay or lesbian as a form of gender inversion. It was thought that same sex attraction meant the person was actually the opposite gender and trapped in the wrong body.