The Sandy Hook Elementary School shooting occurred on December 14, 2012, in Newtown, Connecticut, United States, when 20-year-old Adam Lanza shot and killed 26 people. Twenty of the victims were children between six and seven years old, and six were adult staff members. Earlier that day, before driving to the school, he shot and killed his mother at their Newtown home. As first responders arrived at the school, Lanza committed suicide by shooting himself in the head.

The incident is the deadliest mass shooting at an elementary school in U.S. history, and the fourth-deadliest mass shooting overall. The shooting prompted renewed debate about gun control in the United States, including proposals to make the background-check system universal, and for new federal and state gun legislation banning the sale and manufacture of certain types of semi-automatic firearms and magazines which can hold more than ten rounds of ammunition.

A November 2013 report issued by the Connecticut State Attorney's office concluded that Lanza acted alone and planned his actions, but provided no indication why he did so, or why he targeted the school. A report issued by the Office of the Child Advocate in November 2014 said that Lanza had Asperger syndrome and as a teenager had depression, anxiety and obsessive-compulsive disorder, but concluded that they had "neither caused nor led to his murderous acts." The report went on to say, "his severe and deteriorating internalized mental health problems ... combined with an atypical preoccupation with violence ... (and) access to deadly weapons ... proved a recipe for mass murder."