On December 7, 2017, a school shooting occurred at Aztec High School in Aztec, New Mexico, United States. The perpetrator, William Atchison, a 21-year-old former student of Aztec High, entered the school disguised as a student and hid in the school restroom. He was discovered by student Francisco Fernandez, whom he then shot and killed, before killing another student in the hallway. He attempted to enter a classroom, but a teacher barricaded the door with a couch, preventing him from entering. Atchison then killed himself.

Atchison was prolific online, including on neo-Nazi and white nationalist websites. In March 2016, he was investigated by the Federal Bureau of Investigation (FBI) for threatening to commit a mass shooting. The same year, he was in contact with the eventual perpetrator of the 2016 Munich shooting, who killed nine people in Germany later that year. The FBI dropped their investigation after they determined that Atchison, at the time he was investigated, did not own a firearm, and after he convinced them that his threats were merely "trolling". He bought the gun used in the shooting in November 2017.

The motive for the shooting is disputed, with the Southern Poverty Law Center arguing the shooting was motivated by far-right extremism and incel ideology, while the sheriff's office stated that there was no evidence the shooting was related to Atchison's views, instead arguing that he had personal problems and wanted to kill people for fame. After the shooting, the mother of one of the victims sued the FBI, the Aztec police, and the school district in two lawsuits for failing to prevent the attack; the lawsuit against the FBI was dismissed. The German police were separately criticized for failing to investigate the tie after the Munich shooting. The state of New Mexico authorized additional funding for school safety in response to the shooting.

Aztec is a small town in San Juan County, in northwest New Mexico near the Navajo Nation. The town is located in the heart of the San Juan Basin, which is known for its petroleum and natural gas deposits. Aztec is about three hours away by car, at a distance of approximately 180 miles (290 km) from Albuquerque, the most populous city in New Mexico. In 2017, the town had a population of about 6,500 people, with 900 students enrolled at Aztec High School. According to the United States Department of Education, in 2013, Aztec's student body was measured at 26% Hispanic and almost 20% Native American.

William Edward Atchison was born on March 18, 1996. He lived in Belen, New Mexico, before moving to Aztec with his family, and attending Aztec High School. According to his father, Atchison was bullied in school; in one incident, he was allegedly attacked during a welding class and stabbed in the chest. A neighbor called the Aztec police on Atchison twice, once for firing his airsoft pellet gun at their dogs, and a second time for threatening to shoot her husband during an argument over cannabis that had been found near the property. Because of these disputes, the neighbor refused to allow her sons to play with Atchison. She described him as someone who spent "a lot of time inside and alone", while a coworker said he was bullied.

Atchison was suspended from high school on March 9, 2012, for using the classroom whiteboard to write a chronology of the Columbine High School massacre. This complaint was not reported to the school's resource officer. Atchison had attended sessions with school counselors for many years and was seeing one regularly in Farmington until the counselor retired. He saw a new counselor two more times, but suddenly stopped before dropping out of school on August 20 of the same year. He never returned to school after the suspension. After leaving school, Atchison worked at a local Giant gas station near his home.

Atchison was noted to have a substantial online presence, which The Daily Beast said resulted in him "making many enemies". His online activity included writing pro-Hitler and pro-Trump posts online and frequenting internet forums and white supremacist websites. He used various usernames, including "Future Mass Shooter" and names styled after several mass murderers. He was a sysop of Encyclopedia Dramatica, where he went by "AlGore", though he was sometimes criticized by its userbase. Other users would often ask Atchison "how his manifesto was going". His father later told investigators that he had noticed his son visiting "neo-Nazi" websites and believed they were a negative influence on him. He had few friends outside of the internet.

In an online posting written on the website Think Atheist in 2014, he described his frustration with life in rural New Mexico and his bleak career prospects and asked for advice on how to fix his life, saying: "Look, I'm sorry if I'm rude and hateful or anything, but I don't know what to do. I've lived no life for nearly 19 years [...] How can I become polite and make some friends out there in this world?" Though the post had several hundred views, no one responded. He was a white supremacist; he expressed an interest in mass shooters, Satan, and Hitler, and expressed antisemitic and misogynist sentiments. He also repeatedly posted about wanting to end his own life and called himself "mentally ill", saying he had "major depression, inability to feel joy, intense levels of sadistic desire and various addictions to substances", though other posts evidenced narcissistic thought.