The Mayerthorpe tragedy occurred on March 3, 2005, on the farm of James Roszko, approximately 11 km (6.8 mi) north of Rochfort Bridge near the town of Mayerthorpe in the Canadian province of Alberta.

Roszko shot and killed four Royal Canadian Mounted Police (RCMP) constables: Anthony Gordon, Lionide "Leo" Johnston, Brock Myrol and Peter Schiemann. He then committed suicide. The attack occurred as the officers were executing a search warrant for stolen property and a marijuana-growing operation on the farm. Two individuals who were not present at the shooting, Shawn Hennessey and Dennis Cheeseman, pled guilty to manslaughter for assisting Roszko to return to his farm.

The incident was the worst one-day loss of life for the RCMP since five officers drowned on June 7, 1958, and the worst multiple-officer killing in contemporary Canadian history.