Perthshire (locally: [ˈpɛrθʃər] ; Scottish Gaelic: Siorrachd Pheairt), officially the County of Perth, is a historic county and registration county in central Scotland. Geographically it extends from Strathmore in the east, to the Pass of Drumochter in the north, Rannoch Moor and Ben Lui in the west, and Aberfoyle in the south; it borders the counties of Inverness-shire and Aberdeenshire to the north, Angus to the east, Fife, Kinross-shire, Clackmannanshire, Stirlingshire and Dunbartonshire to the south and Argyllshire to the west. It was a local government county from 1890 to 1930.

Perthshire is known as the "big county", or "the Shire", due to its roundness and status as the fourth largest historic county in Scotland. It has a wide variety of landscapes, from the rich agricultural straths in the east, to the high mountains of the southern Highlands.