The British Army is the principal land warfare force of the United Kingdom, a part of the British Armed Forces along with the Royal Navy and the Royal Air Force. As of 2022, the British Army comprises 79,380 regular full-time personnel, 4,090 Gurkhas, and 28,330 volunteer reserve personnel.

The modern British Army traces back to 1707, with antecedents in the English Army and Scots Army that were created during the Restoration in 1660. The term British Army was adopted in 1707 after the Acts of Union between England and Scotland. Members of the British Army swear allegiance to the monarch as their commander-in-chief, but the Bill of Rights of 1689 and Claim of Right Act 1689 require parliamentary consent for the Crown to maintain a peacetime standing army. Therefore, Parliament approves the army by passing an Armed Forces Act at least once every five years. The army is administered by the Ministry of Defence and commanded by the Chief of the General Staff.

The British Army, composed primarily of cavalry and infantry, was originally one of two Regular Forces within the British military (those parts of the British Armed Forces tasked with land warfare, as opposed to the naval forces), with the other having been the Ordnance Military Corps (made up of the Royal Artillery, Royal Engineers, and the Royal Sappers and Miners) of the Board of Ordnance, which along with the originally civilian Commissariat Department, stores and supply departments, as well as barracks and other departments were absorbed into the British Army when the Board of Ordnance was abolished in 1855. Various other civilian departments of the board were absorbed into the War Office.

The British Army has seen action in major wars between the world's great powers, including the Seven Years' War, the American Revolutionary War, the Napoleonic Wars, the Crimean War and the First and Second World Wars. Britain's victories in most of these decisive wars allowed it to influence world events and establish itself as one of the world's leading military and economic powers. Since the end of the Cold War, the British Army has been deployed to a number of conflict zones, often as part of an expeditionary force, a coalition force or part of a United Nations peacekeeping operation.