Fronted by two immense guns from Royal Navy battleships, the IWM focuses on British military history since 1914. The central atrium display of objects bearing "witness to war" (everything from a Harrier Jump Jet to a battle-scarred press Land Rover) branches into immersive and sensitive exhibitions on the First and Second World Wars, modern warfare, the Holocaust, and more. The same institution owns the HMS Belfast (South Bank), Cabinet War Rooms (Westminster), and Duxford Air Museum (Cambridgeshire - a day trip from London).

The Imperial War Museum , currently branded "Imperial War Museums", is a British national museum. Its headquarters are in London, with five branches in England. Founded as the Imperial War Museum in 1917, it was intended to record the civil and military war effort and sacrifice of the United Kingdom and its Empire during the First World War. The museum's remit has since expanded to include all conflicts in which British or Commonwealth forces have been involved since 1914. As of 2012, the museum aims "to provide for, and to encourage, the study and understanding of the history of modern war and 'wartime experience'." Originally housed in the Crystal Palace at Sydenham Hill, the museum opened to the public in 1920. In 1924, it moved to space in the Imperial Institute in South Kensington and in 1936 it acquired a permanent home at the former Bethlem Royal Hospital in Southwark, which serves as its headquarters. The outbreak of the Second World War saw the museum expand both its collections and its terms of reference, but in the post-war period it entered a period of decline. In 1976 the museum opened IWM Duxford at Duxford airfield in Cambridgeshire, and in 1978 the Royal Navy cruiser HMS Belfast, which is permanently berthed on the River Thames in central London, became a branch of the museum. In 1984, Churchill War Rooms, an underground wartime command centre in Westminster, were opened to the public. In 2002 IWM North opened in Trafford, Greater Manchester, the fifth branch of the museum and the first in the north of England. From the 1980s onwards, the museum's Southwark building underwent a series of multimillion-pound redevelopments, the latest of which was completed in 2022. The museum's collections include archives of personal and official documents, photographs, film and video material, and oral history recordings, an extensive library, a large art collection, and examples of military vehicles and aircraft, equipment, and other artefacts. The museum is funded by government grants, charitable donations, and revenue generation through commercial activity such as retailing, licensing, and publishing. General admission is free to IWM London and IWM North, but an admission fee is levied at the other branches. The museum is an exempt charity under the Charities Act 1993 and a non-departmental public body under the Department for Culture, Media and Sport. As of April 2024, the chairman of the trustees is Guy Weston. Since May 2023, Caro Howell has served as the museum's director-general.