The Woolwich Arsenal was an armaments manufacturing facility on the south bank of the River Thames in Woolwich in south-east London. It was formally established as an Ordnance Storage Depot in 1671 on a 31 acre (125,000 m²) site, the Warren in Tower Place. An ammunition laboratory (the Royal Laboratory) was added in 1695, and a gun foundry (the Royal Brass Foundry) was established in 1717.

In 1805, during the reign of King George III, it became known as the Royal Arsenal. (By this time, Woolwich was already a busy military centre, with the Woolwich Dockyard to the west of the Arsenal, and the Royal Military Academy and the headquarters of the Royal Artillery next to each other to the south.)

Several buildings within the Arsenal are attributed to architect Sir John Vanbrugh.

The Arsenal was a renowned centre of excellence in mechanical engineering, with notable engineers including Samuel Bentham, Marc Isambard Brunel and Henry Maudslay employed there. It also became a noted research facility, developing several key advances in armament design and manufacture.

In 1886 workers at the Arsenal formed a football club initially known as Dial Square after the workshops in the heart of the complex, playing their first game on 11 December (a 6-0 victory over East Wanderers) at Plumstead Common. Renamed Royal Arsenal two weeks later (and also known as the 'Woolwich Reds'), the club entered the professional football league as Woolwich Arsenal in 1893. Today it is known simply as Arsenal F.C., having moved to north London in 1913.

At its peak, during World War I, the Royal Arsenal extended over some 1300 acres (5.3 km²) and employed around 80,000 people.

The Ordnance Factories closed in 1967 and it ceased to be a military establishment in 1994. The sprawling Arsenal site is now one of the focal points for redevelopment in the Thames Gateway zone, but the links to its historic past are not lost. Many notable buildings are being retained in the redevelopment, and the site includes a museum (Firepower!) telling the story of the Royal Arsenal.