A hate group is a social group that advocates and practices hatred, hostility, or violence towards members of a race, ethnicity, nation, religion, gender, gender identity, sexual orientation, or any other designated sector of society.

According to the United States Federal Bureau of Investigation (FBI), a hate group's "primary purpose is to promote animosity, hostility, and malice against persons belonging to a race, religion, disability, sexual orientation, or ethnicity/national origin which differs from that of the members of the organization."

In the US, the FBI does not publish a list of hate groups, and it also says that "investigations are only conducted when a threat or advocacy of force is made; when the group has the apparent ability to carry out the proclaimed act; and when the act would constitute a potential violation of federal law". The FBI maintains statistics on hate crimes.

Two private American non-profit organizations that monitor intolerance and hate groups are the Anti-Defamation League (ADL) and the Southern Poverty Law Center (SPLC). They maintain lists of what they deem to be hate groups, supremacist groups and antisemitic, anti-government or extremist groups that have committed hate crimes. The SPLC's definition of a "hate group" includes any group with beliefs or practices that attack or malign an entire class of people—particularly when the characteristics being maligned are immutable. However, at least for the SPLC, inclusion of a group in the list "does not imply a group advocates or engages in violence or other criminal activity." According to USA Today, their list ranges from "white supremacists to black nationalists, neo-Nazis to neo-Confederates."

The Canadian Anti-Hate Network is a nonprofit organization that monitors hate groups in Canada.

According to the SPLC, from 2000 to 2008, hate group activity saw a 50 percent increase in the US, with a total of 926 active groups. In 2019, the organization's report showed a total of 1,020 hate groups, the highest number in 20 years, and a 7% increase from 2017 to 2018. The previous high was 1,018 in 2011, and the recent low point was 2014, when the list included 784 groups. A rise in white nationalist groups from 100 in 2017 to 148 in 2018 was the most significant increase in the 2019 report.

Since 2010 the term alt-right, short for "alternative right", has come into usage. This broad term includes a range of people who reject mainstream conservatism in favor of forms of conservatism that may embrace implicit or explicit racism or white supremacy. The alt-right is described as being "a weird mix of old-school neo-Nazis, conspiracy theorists, anti-globalists, and young right-wing internet trolls—all united in the belief that white male identity is under attack by multicultural, "politically correct" forces."

Four categories which are associated with hate groups' propensity for violence are: organizational capacity, organizational constituency, strategic connectivity, and structural arrangement. The larger an extremist group is and the longer it has existed, it is more prone to engage in violence. Regionally, hate groups which are based in the West and the Northeast are more likely to engage in violence than those hate groups which are based in the South. If a group has a charismatic leader, it is more likely to be violent. Groups that share conflict-based relationships with other groups are more likely to engage in extreme violence. The amount of ideological literature which a group publishes is linked to significant decreases in a group's violent behavior, with more literature linked to lower levels of violence.