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.

A mass shooting is a violent crime in which one or more attackers kill or injure multiple individuals simultaneously using a firearm. There is no widely accepted definition of "mass shooting" and different organizations tracking such incidents use different definitions. Definitions of mass shootings exclude warfare and sometimes exclude instances of gang violence, armed robberies, familicides and terrorism. The perpetrator of an ongoing mass shooting may be referred to as an active shooter.