The history of the British Army spans over three and a half centuries since its founding in 1660 and involves numerous European wars, colonial wars and world wars. From the late 17th century until the mid-20th century, the United Kingdom was the greatest economic and imperial power in the world, and although this dominance was principally achieved through the strength of the Royal Navy, RN, the British Army played a significant role.

As of 2015, there were 92,000 professionals in the regular army including 2,700 Gurkhas and 20,480 Volunteer Reserves. Britain has generally maintained only a small regular army during peacetime, expanding this as required in time of war, due to Britain's traditional role as a sea power.