Homophobia encompasses a range of negative attitudes and feelings toward homosexuality or people who are identified or perceived as being lesbian, gay, bisexual or transgender (LGBT). It can be expressed as antipathy, contempt, prejudice, aversion, or hatred, and may be based on irrational fear.

Homophobia is observable in critical and hostile behavior such as discrimination and violence on the basis of sexual orientations that are non-heterosexual. According to the 2010 Hate Crimes Statistics released by the FBI National Press Office, 19.3 percent of hate crimes across the United States "were motivated by a sexual orientation bias." Moreover, in a Southern Poverty Law Center 2010 Intelligence Report extrapolating data from fourteen years (1995–2008), which had complete data available at the time, of the FBI's national hate crime statistics found that LGBT people were "far more likely than any other minority group in the United States to be victimized by violent hate crime."

Recognized types of homophobia include institutionalized homophobia, e.g. religious homophobia and state-sponsored homophobia, and internalized homophobia, experienced by people who have same-sex attractions, regardless of how they identify. Forms of homophobia toward identifiable LGBT social groups have similar yet specific names: lesbophobia – the intersection of homophobia and sexism directed against lesbians, biphobia – towards bisexuality and bisexual people, and transphobia, which targets transsexualism, transsexual and transgender people, and gender variance or gender role nonconformity.