Lanarkshire, also called the County of Lanark (Scottish Gaelic: Siorrachd Lannraig; Scots: Lanrikshire), is a historic county, lieutenancy area and registration county in the Central Lowlands of Scotland. The county is no longer used for local government purposes, but gives its name to the two modern council areas of North Lanarkshire and South Lanarkshire.

The county was established as a shire (the area controlled by a sheriff) in the twelfth century, covering most of the basin of the River Clyde. The area was sometimes known as Clydesdale. In the early fifteenth century the western part of the shire was removed to become Renfrewshire. The historic county of Lanarkshire includes Glasgow, but the city had a separate lieutenancy from 1893. A Lanarkshire County Council existed from 1890 until 1975, which was based in Glasgow until 1964 when it moved to Hamilton.

Lanarkshire is generally bounded to the north by Dunbartonshire and Stirlingshire, to the north-east by West Lothian and Midlothian, to the east by Peeblesshire, to the south by Dumfriesshire, and to the west by Ayrshire and Renfrewshire. The county is more rural in the south where it extends into the hills of the Southern Uplands, and more built-up in the north where it includes much of the Greater Glasgow conurbation, Scotland's largest urban area.