The Buffs (Royal East Kent Regiment), formerly the 3rd Regiment of Foot, was a line infantry regiment of the British Army traditionally raised in the English county of Kent and garrisoned at Canterbury. It had a history dating back to 1572 and was one of the oldest regiments in the British Army, being third in order of precedence (ranked as the 3rd Regiment of the line). The regiment provided distinguished service over a period of almost four hundred years accumulating one hundred and sixteen battle honours. In 1881, under the Childers Reforms, it was known as the Buffs (East Kent Regiment) and later, on 3 June 1935, was renamed the Buffs (Royal East Kent Regiment).

In 1961, it was amalgamated with the Queen's Own Royal West Kent Regiment to form the Queen's Own Buffs, The Royal Kent Regiment, which was later merged, on 31 December 1966, with the Queen's Royal Surrey Regiment, the Royal Sussex Regiment and the Middlesex Regiment (Duke of Cambridge's Own) to form the Queen's Regiment. This regiment was, in turn, amalgamated with the Royal Hampshire Regiment, in September 1992, to create the Princess of Wales's Royal Regiment (Queen's and Royal Hampshires).

The Dutch fight for independence from Spain in the 1568–1648 Eighty Years' War was supported by Protestants across Europe; the origins of the regiment were Thomas Morgan's Company of Foot, a group of 300 volunteers from the London Trained Bands formed in 1572. In 1586, these English and Scottish volunteer units were brought together in the Anglo-Scots Brigade, which in various formats served in the Dutch military until 1782.

When the Second Anglo-Dutch War started in 1665, the Brigade's units were ordered to swear loyalty to the Stadtholder and those who disobeyed were cashiered. Using his own funds, Sir George Downing, the English ambassador to the Netherlands, raised the Holland Regiment from the starving remnants of those who refused to sign. In 1665, it was known as the 4th (The Holland Maritime) Regiment and by 1668 as the 4th (The Holland) Regiment.

When the Third Anglo-Dutch War began in 1672, the Duke of Buckingham was authorised to recruit an additional eight companies but the two countries made peace in the February 1674 Treaty of Westminster. These men were incorporated into the Anglo-Scots Dutch Brigade and fought in the 1672–1678 Franco-Dutch War; in November 1688, it accompanied William III to England. It was transferred onto the English military establishment as the "4th The Lord High Admiral's Regiment" and in 1689 became the 3rd (Prince George of Denmark's) Regiment of Foot. During the 1689–1697 Nine Years War, it served in the Low Countries, including the battles of Walcourt, Steenkerque and Landen. It returned to England when the war ended with the 1697 Treaty of Ryswick.

During the War of the Spanish Succession, it served in Marlborough campaigns, including the battles of Blenheim, Ramillies, Malplaquet and Oudenarde, before returning to England in August 1714. Until the 1751 reforms, units were commonly named after their current colonel; it reverted to this practice when Prince George of Denmark died in 1708, although it was also referred to as the 'Holland Regiment' or "Buffs" after its coat facings. It was also sometimes called "The Old Buffs", to distinguish it from "The Young Buffs", the 31st Foot.

Apart from the 1719 Vigo expedition, the next 25 years were spent on garrison duty in England and Scotland. It returned to Flanders in 1742 during the War of the Austrian Succession, as Thomas Howard's regiment; to distinguish it from that led by Sir Charles Howard, one became the "Buffs", and the other the Green Howards. It fought at the Battle of Dettingen in June 1743 and at the Battle of Fontenoy in May 1745. With the outbreak of the 1745 Rising, it was sent to Scotland, taking part in the Battle of Falkirk Muir in January 1746 and Battle of Culloden in April 1746. It returned to the Netherlands in April 1747 and saw action at the Battle of Lauffeld in July.

Following the 1748 Treaty of Aix-la-Chapelle, it spent the next ten years on garrison duty in England; in 1751, it was retitled the 3rd Regiment of Foot, "The Buffs". The Seven Years' War began in 1756; in autumn 1758, the regiment was posted to the West Indies, taking part in the January 1759 attacks on Martinique and Guadeloupe. After returning home, it took part in the capture of Belle Île in June 1761. It then moved to Portugal and fought at the Battle of Valencia de Alcántara in August 1762 before returning to England in spring 1771.