Heteronormativity is the belief that everyone is heterosexual by nature, and every other form of human sexuality is not as good as heterosexuality, or even an illness that needs to be fixed. In a heteronormative system, there are two strict genders, men and women, and everyone must behave according to their gender role in society. A heteronormative view of the world believes that a person's sex decides their sexuality, gender identity and gender roles.
Homophobia, transphobia, and heterosexism could not exist without heteronormativity.
According to queer theory, societies force heteronormativity on people it does not fit, such as LGBT people, queer people, and intersex people.