Heteronormativity is the definition of heterosexuality as the normative human sexuality. It assumes the gender binary (i.e., that there are only two distinct, opposite genders) and that sexual and marital relations are most fitting between people of the opposite sex.

Heteronormativity creates and upholds a social hierarchy based on sexual orientation with the practice and belief that heterosexuality is deemed as the societal norm. A heteronormative view, therefore, involves alignment of biological sex, sexuality, gender identity and gender roles. Heteronormativity has been linked to heterosexism and homophobia, and the effects of societal heteronormativity on lesbian, gay and bisexual individuals have been described as heterosexual or "straight" privilege.

Michael Warner popularized the term in 1991, in one of the first major works of queer theory. The concept's roots are in Gayle Rubin's notion of the sex/gender system and Adrienne Rich's notion of compulsory heterosexuality. From the outset, theories of heteronormativity included a critical look at gender; Warner wrote that "every person who comes to a queer self-understanding knows in one way or another that her stigmatization is intricated with gender. ... Being queer ... means being able, more or less articulately, to challenge the common understanding of what gender difference means." Lauren Berlant and Warner further developed these ideas in their seminal essay "Sex in Public":

Heteronormativity is more than ideology, or prejudice, or phobia against gays and lesbians; it is produced in almost every aspect of the forms and arrangements of social life: nationality, the state, and the law; commerce; medicine; and education; as well as in the conventions and affects of narrativity, romance, and other protected spaces of culture.

Modern family structures in the past and present vary from what was typical of the 1950s nuclear family. In the United States, the families of the second half of the 19th century and early 20th century were characterized by the death of one or both parents for many American children. In 1985, the United States is estimated to have been home to approximately 2.5 million post-divorce, stepfamily households containing children. During the late 1980s, almost 20% of families with children headed by a married couple were stepfamilies.

Over the past three decades, rates of divorce, single parenting, and cohabitation have risen precipitously. Nontraditional families (which diverge from "a middle-class family with a bread-winning father and a stay-at-home mother, married to each other and raising their biological children") constitute the majority of families in the United States and Canada today. Shared Earning/Shared Parenting Marriage (also known as Peer Marriage) where two heterosexual parents are both providers of resources and nurturers to children has become popular. Modern families may also have single-parent headed families which can be caused by divorce, separation, death, families who have two parents who are not married but have children, or families with same-sex parents. With artificial insemination, surrogate mothers, and adoption, families do not have to be formed by the heteronormative biological union of a male and a female.

The consequences of these changes for the adults and children involved are heavily debated. In a 2009 Massachusetts spousal benefits case, developmental psychologist Michael Lamb testified that parental sexual orientation does not negatively affect childhood development. "Since the end of the 1980s... it has been well established that children and adolescents can adjust just as well in nontraditional settings as in traditional settings," he argued. However, columnist Maggie Gallagher argues that heteronormative social structures are beneficial to society because they are optimal for the raising of children. Australian-Canadian ethicist Margaret Somerville argues that "giving same-sex couples the right to found a family unlinks parenthood from biology". Recent criticisms of this argument have been made by Timothy Laurie, who argues that both intersex conditions and infertility rates have always complicated links between biology, marriage, and child-rearing.

Heteronormative temporality, a subset of heteronormativity, posits that the ideal societal trajectory involves achieving heterosexual marriage as life's ultimate goal. This ideology imposes societal expectations that encourage individuals to conform to traditional roles within a nuclear family structure: seeking an opposite-sex partner, entering into heterosexual marriage, and raising children. Heteronormative temporality promotes abstinence-only until marriage. Many American parents adhere to this heteronormative narrative and teach it to their children. According to Amy T. Schalet, it seems that the bulk of parent-child sex education revolves around abstinence-only practices in the United States, but this differs in other parts of the world. Similarly, George Washington University Professor, Abby Wilkerson, discusses how the healthcare and medicinal industries reinforce the views of heterosexual marriage to promote heteronormative temporality. The concept of heteronormative temporality extends beyond heterosexual marriage to include a pervasive system where heterosexuality is seen as a standard, and anything outside of that realm is not tolerated. Wilkerson explains that it dictates aspects of everyday life such as nutritional health, socio-economic status, personal beliefs, and traditional gender roles.