Columbine High School Massacre, Littleton, Colo., 1999

A school shooting and attempted bombing occurred at Columbine High School in Columbine, Colorado, United States, on April 20, 1999. The perpetrators, twelfth-grade students Eric Harris and Dylan Klebold, murdered 13 students and one teacher; ten were killed in the school library, where Harris and Klebold subsequently died by suicide. Twenty additional people were injured by gunshots, and gunfire was exchanged several times with law enforcement with neither side being struck. Another three people were injured trying to escape. The Columbine massacre was the deadliest mass shooting at a K–12 school in U.S. history until December 2012. It is still considered one of the most infamous massacres in the United States, and it is known for inspiring many other school shootings and bombings; the word Columbine has since become a byword for modern school shootings. As of 2025, Columbine remains the deadliest mass shooting and school shooting in Colorado, the deadliest high school shooting to happen west of the Mississippi River, and one of the deadliest mass shootings in the United States. Harris and Klebold, who planned for roughly a year, intended the attack to be primarily a bombing and only secondarily a shooting. The pair launched a shooting attack after the homemade bombs they planted in the school failed to detonate. Their motive remains uncertain. The police were slow to enter the school and were heavily criticized for not intervening during the shooting. The incident resulted in the introduction of the immediate action rapid deployment (IARD) tactic, which is used in active-shooter situations, and an increased emphasis on school security with zero-tolerance policies. The violence sparked debates over American gun culture and gun control laws, high school cliques, subcultures (e.g. goths), outcasts, and school bullying, as well as teenage use of pharmaceutical antidepressants, the Internet, and violence in video games and film. Many makeshift memorials were created after the massacre, including ones using victim Rachel Scott's car and John Tomlin's truck. Fifteen crosses for the victims and the shooters were erected on top of a hill in Clement Park. The crosses for Harris and Klebold were later removed after controversy. The planning for a permanent memorial began in June 1999, and the resulting Columbine Memorial opened to the public in September 2007. As of June 2025, the shooting has inspired more than 70 copycat attacks, and its impact has been dubbed the Columbine effect.