The Port Arthur massacre was a mass shooting that occurred on 28 April 1996 at Port Arthur, a tourist town in the Australian state of Tasmania. The perpetrator, Martin Bryant, killed 35 people and wounded 23 others, the deadliest massacre in modern Australian history. The attack led to fundamental changes in Australia's gun laws.

Two of Bryant's victims were known to him personally and were killed at Seascape, a bed and breakfast property. The majority of his victims were killed in a shooting spree at the Port Arthur Historic Site, a popular tourist destination. Using two semi-automatic rifles, he began his attack at a small café before moving into a nearby gift shop, killing twenty people indiscriminately in a short amount of time. Many others were killed at the site's car park, including several children. After killing its four occupants, Bryant stole a vehicle at the site's tollbooth and drove to a nearby service station, where he killed a woman and abducted her partner. He continued to fire at passing vehicles before finally returning to Seascape with his hostage, who was then killed. He set fire to the property but was captured the following morning.

Bryant pleaded guilty to the killings and received 35 life sentences without parole; his motives have been subject to debate. The massacre led to a reassessment of Australia's gun laws by the newly elected Howard government. The National Firearms Agreement between state and federal governments was announced within two weeks of the massacre, establishing heavy restrictions on the use of automatic and semi-automatic weapons and creating a gun buyback program, a national gun registry and a waiting period for firearm sales.