The Royal Regiment of Horse Guards (The Blues) (RHG) was a cavalry regiment of the British Army, part of the Household Cavalry.

Founded in August 1650 at Newcastle upon Tyne and County Durham by Sir Arthur Haselrig on the orders of Oliver Cromwell as the Regiment of Cuirassiers, also known as the London lobsters, the regiment became the Earl of Oxford's Regiment during the reign of King Charles II. As the regiment's uniform was blue in colour at the time, it was nicknamed "the Oxford Blues", from which was derived the nickname the "Blues." In 1750 the regiment became the Royal Horse Guards Blue and eventually, in 1877, the Royal Horse Guards (The Blues).

The regiment served in the French Revolutionary Wars and in the Peninsular War. Two squadrons fought, with distinction, in the Household Brigade at the Battle of Waterloo. In 1918, the regiment served as the 3rd Battalion, Guards Machine Gun Regiment. During the Second World War the regiment was part of the Household Cavalry Composite Regiment. The Royal Horse Guards was amalgamated with the Royal Dragoons (1st Dragoons) to form the Blues and Royals(Royal Horse Guards and 1st Dragoons) in 1969.

The Blues were at Windsor when war was declared on 3 September 1939. That month, the Life Guards and Royal Horse Guards formed the Household Cavalry Composite Regiment and the Household Cavalry Training Regiment. The Household Cavalry Composite Regiment, which saw action in Palestine, Iraq and North Africa, disbanded in 1945 and the personnel returned to their original units.