This is a list of mass shootings in the United States that have occurred in 2021. Mass shootings are incidents involving several victims of firearm-related violence. The precise inclusion criteria are disputed, and there is no broadly accepted definition. As of December 2021, 693 (of which 303 resulted in zero deaths) fit the Mass Shooting Tracker project criterion, leaving 703 people dead and 2,842 injured, for a total of 3,545 total victims, some including the shooter(s).