On July 20, 2012, a mass shooting occurred inside a Century 16 movie theater in Aurora, Colorado, United States, during a midnight screening of the film The Dark Knight Rises. 24-year-old James Eagan Holmes set off tear gas grenades and shot into the audience with multiple firearms. Twelve people were killed and 70 others were injured, 58 of them due to gunfire.

Holmes was arrested minutes later in his car outside the cinema. Earlier, he had rigged his apartment with homemade explosives and incendiary devices. These were defused by the Arapahoe County Sheriff's Office Bomb Squad a day after the shooting.

Fearing copycat crimes, movie theaters showing the same film across the United States increased their security. Gun sales increased in Colorado, and political debates were generated about gun control in the United States.

Holmes confessed to the shooting but pleaded not guilty by reason of insanity. Arapahoe County prosecutors sought the death penalty. The trial began on April 27, 2015. On July 16 of that year, Holmes was convicted of 24 counts of first-degree murder, 140 counts of attempted first-degree murder, and one count of possessing explosives. On August 7, the jury deadlocked on whether to impose the death penalty. On August 26, Holmes was given 12 life sentences, one for every person he killed; he also received 3,318 years for the attempted murders of those he wounded and for rigging his apartment with explosives.

The shooting occurred in Theater 9 at the Century 16 multiplex (operated by Cinemark Theatres), located in the Town Center at Aurora shopping mall at 14300 E. Alameda Avenue. Police said that Holmes bought a ticket, entered the theater, and sat in the front row. About 20 minutes into the film, he left theater 9 through an emergency exit door beside the movie screen, with direct access to the lightly used parking area at the back of the complex, while propping the door slightly open with a plastic tablecloth holder. There were about 400 people inside theater 9.

Holmes went to his car (which he had parked near the exit door), changed into protective clothing, and retrieved his guns. About 30 minutes into the movie, police say, around 12:30 a.m., he reentered the theater through the exit door. Holmes was dressed in black and wore a gas mask, a load-bearing vest, a ballistic helmet, bullet-resistant leggings, a bullet-resistant throat protector, a groin protector, and tactical gloves. He was listening to a techno radio station, which was playing the song "Becoming Insane" by Infected Mushroom, through a set of headphones so that he could not hear anything from people in the theater. Initially, few in the audience considered Holmes to be a threat. Some witnesses thought he was wearing a costume, like other audience members who had dressed up for the screening. Some believed he was playing a prank, while others thought he was part of a special effects setup for the film's premiere, or a publicity stunt by the studio or theater management.

Holmes reportedly threw one canister towards the left side of the theatre, emitting a gas or smoke, that partially obscured the audience members' vision, made their throats and skin itch, and caused eye irritation. He fired a 12-gauge Remington 870 Express Tactical shotgun, first at the ceiling and then at the audience. He also fired a Smith & Wesson M&P15 semi-automatic rifle with a 100-round drum magazine, which eventually malfunctioned. Finally, he fired a .40-caliber Glock 22 Gen4 handgun. He shot first to the back of the room, and then toward people in the aisles. A bullet passed through the wall and hit three people in adjacent theater 8, which was screening the same film. Witnesses said the multiplex's fire alarm system began sounding soon after the attack began, and staff told people in Theater 8 to evacuate.

Holmes fired 76 shots in the theater: 6 from the shotgun, 65 from the semi-automatic rifle, and 5 from the .40-caliber handgun.