Mass shootings are incidents involving multiple victims of firearm related violence. Definitions vary, with no single, broadly accepted definition. One definition is an act of public firearm violence—excluding gang killings, domestic violence, or terrorist acts sponsored by an organization—in which a shooter kills at least four victims. Using this definition, a 2016 study found that nearly one-third of the world's public mass shootings between 1966 and 2012 (90 of 292 incidents) occurred in the United States. In 2017, The New York Times recorded the same total of mass shootings for that span of years.
Perpetrator demographics vary by type of mass shooting, though in almost all cases they are male. Contributing factors may include easy access to guns, perpetrator suicidality and life history factors, and sociocultural factors including media reporting of mass shootings and declining social capital. However, reliable statistical generalizations about mass shootings are difficult to establish due to the absence of a universal definition for mass shootings, sources for data on mass shootings being incomplete and likely including biased samples of incidents, and mass shootings having low base rates.
The Federal Bureau of Investigation designated 61 of all events in 2021 as active shooter incidents. The United States has had more mass shootings than any other country. After a shooting, perpetrators generally either commit suicide or are restrained or killed by law enforcement officers. Mass shootings accounted for under 0.2% of gun deaths in the United States between 2000 and 2016, and less than 0.5% of all homicides in the United States from 1976 to 2018.
Definitions There is no fixed definition of a mass shooting in the United States, and different researchers define "mass shootings" in different ways.Jon Greenberg, Joe Biden said mass shootings tripled when the assault weapon ban ended. They did , PolitiFact (May 25, 2022). Of the seven following definitions, most use a minimum of four victims as a threshold. Among the various definitions are those that are:
Based on injuries:
Gun Violence Archive: More broadly defines "mass shooting" to mean four or more (excluding the perpetrator) shot at roughly the same time and location, regardless of number of fatalities or the motive. Brady: United Against Gun Violence uses a similar definition.
Mass Shooting Tracker: Defines "mass shooting" as "an incident where four or more people are shot in a single shooting spree," including the perpetrator or police shootings of civilians around the perpetrator, and irrespective of the motive of the perpetrator or the location of the murders.
Based on number of deaths:
Investigative Assistance for Violent Crimes Act of 2012, signed into law in January 2013: Defines a "mass killing" as the killing of at least three victims, excluding the perpetrator, and regardless of the weapon used.
Everytown for Gun Safety, which tracks mass shootings based on press accounts, police records, and court papers, defines mass shooting as "any incident in which four or more people are shot and wounded or killed, excluding the shooter."
Based on number of deaths and nature of attack:
Congressional Research Service (CRS) 2015 report titled Mass Murder with Firearms: Did not define "mass shooting" but defined "public mass shooting" for the purposes of its report as "a multiple homicide incident in which four or more victims are murdered with firearms, within one event, and in one or more locations in close proximity." The CRS further states that its report "attempts to refine the relatively broad concept of mass shooting...into a narrower formulation: public mass shootings."
Mother Jones's open-source database of mass shootings: The magazine's database, established after the 2012 Aurora movie theater massacre and updated continuously since that time, defines "mass shootings" as "indiscriminate rampages in public places resulting in four or more victims killed by the attacker," excluding "shootings stemming from more conventionally motivated crimes such as armed robbery or gang violence" and shootings in which the perpetrator has not been identified. This definition generally is consistent with the FBI's figures and the data used by criminologists.
2022 National Institute of Justice/The Violence Project dataset: Defines "mass public shooting" as an incident in which at least four victims were killed with firearms in a single event "and the murders are not attributable to any other underlying criminal activity or commonplace circumstance (armed robbery, criminal competition, insurance fraud, argument, or romantic triangle)."Public Mass Shootings: Database Amasses Details of a Half Century of U.S. Mass Shootings with Firearms, Generating Psychosocial Histories , National Institute of Justice/The Violence Project (February 3, 2022).
The FBI defines an "active shooter" incident as "one or more individuals actively engaged in killing or attempting to kill people in a populated area", excluding gun-related incidents that were the result of self-defense, gang or drug violence, residential or domestic disputes, crossfire as a byproduct of another ongoing criminal act, controlled barricade or hostage situations, or actions that appeared not to have put other people in peril.
The appropriateness of a broad versus narrow definition of "mass shooting" has been the subject of debate. Some commentators argue in favor of a narrow definition of mass shootings that excludes the victims of street crime. Mark Follman of Mother Jones, which compiles an open-source database of mass shootings, contends that "While all the victims are important, conflating those many other crimes with indiscriminate slaughter in public venues obscures our understanding of this complicated and growing problem." Northeastern University criminologist James Alan Fox argues against the use of the broad definition of "mass shooting" in the popular press, stating that it misleads readers. Others, by contrast, argue that defining "mass shooting" solely as a shooting in a public place in which the perpetrator fires at random is too narrow. For example, Mark Hay argues that although gang, party, and domestic violence "probably warrant different solutions" than random mass public shootings, a narrow definition fails "to capture and convey the full scope of large-scale gun violence in the United States" and its effect on marginalized communities.
Frequency
As of 2017, studies indicated that the rate at which public mass shootings occur has tripled since 2011. Between 1982 and 2011, a mass shooting occurred roughly once every 200 days. However, between 2011 and 2014, that rate has accelerated greatly with at least one mass shooting occurring every 64 days in the United States.
FBI data shows that active shooter incidents increased from 2000 to 2019. Under the definition used by the Gun Violence Archive, by the end of 2019, there were 417 mass shootings; by the end of 2020, there had been 611; and by the end of 2021, 693. By mid-May 2021, there were 10 mass shootings per week on average; by mid-May 2022, there was a total of 198 mass shootings in the first 19 weeks of the year, which represents 11 mass shootings a week. The FBI designated 61 active shooter incidents. There were ten mass shootings in 2019, two in 2020, and six in 2021. Under the substantially narrower 2022 National Institute of Justice/The Violence Project dataset definition, there were 167 mass shootings (4 or more killed with firearms in public, not connected to "underlying criminal activity or commonplace circumstance") in the U.S. from 1966 to 2019, and 30.8% of the shootings occurred at the workplace.
A comprehensive report by USA Today tracked all mass killings from 2006 through 2017 in which the perpetrator willfully killed four or more people. For mass killings by firearm for instance, it found 271 incidents with a total of 1,358 victims.
In October 2018, PLOS One published a study analyzing 100 mass shootings from the Mother Jones database from January 1982 to May 2018 to evaluate whether mass shootings became more common in the United States over the preceding three decades. It found that mass shootings had steadily increased. However, some researchers dispute whether the frequency of mass shootings is increasing due to differences in research methods and differences in the criteria used to define events as mass shootings.
In 2018 The Washington Post recorded 163 mass shootings in the United States between 1967 and June 2019. Mother Jones recorded 140 mass shootings between 1982 and February 2023.
Under the Everytown for Gun Safety definition ("any incident in which four or more people are shot and wounded or killed, excluding the shooter") there were an average of 463 mass shootings in the U.S. each year from 2015 to 2022. The report found that: "In nearly all mass shootings over this period, the shooter was an adult man who acted alone. Thirty-two percent of mass shooters, or 92 shooters, ended with the perpetrator committing suicide, and another 24 shooters were killed by responding law enforcement. The remaining 145 mass shooters were taken into custody by law enforcement, while the outcomes and identities of 23 remain unknown." In 2022, the Violence Project of the National Institute of Justice recorded 185 mass shootings from 1966 to December 2022. A 2023 report published in The Journal of the American Medical Association (JAMA) covering 2014 to 2022, found there had been 4,011 mass shootings in the US.
Perpetrator demographics
According to The New York Times, there is no common profile of people who carry out mass shootings in the United States, except that they are mostly men. By race, according to a study, the proportion of mass shooters in the United States who are white is about equal to the overall proportion of white people in the general population of the US. The proportion of male mass shooters is considerably larger than the proportion of males in the general population. According to the Associated Press, white men comprise nearly 50% of all mass shooters in the US. According to the National Institute of Justice/The Violence project study, the demographics of shooters were 97.7% male, with an average age of 34.1 years, 52.3% white, 20.9% black, 8.1% Latino, 6.4% Asian, 4.2% Middle Eastern, and 1.8% Native American.
According to the Center for Inquiry, mass shootings of family members (the most common) are usually carried out by white, middle-aged males. Felony-related mass shootings (connected with a previous crime) tend to be committed by young black or Hispanic males with extensive criminal records, typically against people of the same ethnic group. Public mass shootings of persons unrelated to the shooter, and for a reason not connected with a previous crime (the rarest but most publicized) are committed by men whose racial distribution closely matches that of the nation as a whole. Other than gender, the demographic profiles of public mass shooters are too varied to draw firm conclusions. In a 2014 review of 160 active shooter incidents in the U.S. from 2000 to 2013 across 40 states and the District of Columbia, the FBI found that the perpetrator was female in only 6 of the 160 incidents (4%) and that in only 2 incidents (1%) was there more than one perpetrator. Analogously, in December 2013, the Journal of Forensic Sciences published a sociodemographic network characteristics and antecedent behaviors survey of 119 lone-actor terrorists in the United States and Europe that found that 96.6% were male.
Contributing factors
In a 2026 meta-analysis, a study found "consistent patterns in perpetrators’ experiences, behaviors, and communications prior to the attacks." The study, released by the Rockefeller Institute of Government in Albany, New York, reviewed 171 mass shootings in 39 states from 1999 to 2024, had several "Key findings":