21st Regiment of Foot

Royal Scots Fusiliers
Regimental cap badge
Active	1678–1959
Country	Kingdom of Scotland (1678–1688)  Kingdom of England (1688–1707)  Kingdom of Great Britain (1707–1800)  United Kingdom (1801–1959)
Branch	British Army
Type	Infantry
Role	Line infantry
Part of	Lowland Brigade
Garrison/HQ	Churchill Barracks, Ayr
Insignia
Hackle	White
Tartan	Hunting Erskine

The Royal Scots Fusiliers was a line infantry regiment of the British Army that existed from 1678 until 1959 when it was amalgamated with the Highland Light Infantry (City of Glasgow Regiment) to form the Royal Highland Fusiliers (Princess Margaret's Own Glasgow and Ayrshire Regiment) which was later itself merged with the Royal Scots Borderers, the Black Watch (Royal Highland Regiment), the Argyll and Sutherland Highlanders and the Highlanders (Seaforth, Gordons and Camerons) to form a new large regiment, the Royal Regiment of Scotland.

The regiment was raised in Scotland in 1678 by Stuart loyalist Charles Erskine, de jure 5th Earl of Mar for service against the rebel covenanting forces during the Second Whig Revolt (1678–1679). It was used to keep the peace and put down brigands, mercenaries, and rebels. In the Glorious Revolution of 1688, the regiment was ordered south. Initially, it stayed loyal to James II of England; however, when he fled to Ireland, it opted to serve Prince William of Orange.

The regiment was converted to fusiliers in 1685. It was nicknamed the "Duke of Marlborough's Own" for its excellent service in all of the Duke's campaigns in the War of the Spanish Succession.

The regiment was renamed the North British Fusilier Regiment of Foot in 1707 reflecting Treaty of Union that led to the creation of Great Britain.