Defence Intelligence (DI) is an organisation within the United Kingdom intelligence community which focuses on gathering and analysing military intelligence. It differs from the UK's intelligence agencies (MI6, GCHQ and MI5) in that it is an integral part of a government department – the Ministry of Defence (MoD) – rather than a stand-alone organisation. The organisation employs a mixture of civilian and military staff and is funded within the UK's defence budget. The organisation was formerly known as the Defence Intelligence Staff (DIS), but changed its name in 2009.

The primary role of Defence Intelligence is that of 'all-source' intelligence analysis. This discipline draws information from a variety of overt and covert sources to provide the intelligence needed to support military operations, contingency planning, and to inform defence policy and procurement decisions. The maintenance of the ability to give timely strategic warning of politico-military and scientific and technical developments with the potential to affect UK interests is a vital part of the process.

DI's assessments are used outside the MoD to support the work of the Joint Intelligence Committee (JIC) and to assist the work of other Government departments (OGDs) and international partners (such as NATO and the European Union). It is this 'all-source' function which distinguishes Defence Intelligence from other organisations such as SIS and GCHQ, which focus on the collection of 'single-source' Human Intelligence (HUMINT) and Signals Intelligence (SIGINT) respectively. As such Defence Intelligence occupies a unique position within the UK intelligence community.

The organisation is headed by the Chief of Defence Intelligence, currently Adrian Bird, who replaced General James Hockenhull after his appointment as Commander, Strategic Command.

Defence Intelligence can trace its history back to 1873 with the formation of the Intelligence Branch of the British War Office, which, in 1888, became the Directorate of Military Intelligence. The Committee of Imperial Defence, established in 1902, had the task of co-ordinating the different armed services on issues of military strategy intelligence assessments and estimates.

During World War I (1914–1918), Military Intelligence (MI) departments, such as MI1 for the secretariat of the Director of Military Intelligence (now GCHQ), were responsible for various intelligence gathering functions. Many of the original MI departments, such as MI4 (Aerial Photography) were renamed or eventually subsumed into Defence Intelligence.

Shortly after the 1945 end of the Second World War, the topographical department of the War Office was transformed into the Joint Intelligence Bureau (JIB), and its director, Sir Kenneth Strong, became a full member of the Joint Intelligence Committee (JIC) in January 1947. The JIB was structured into a series of divisions: procurement (JIB 1), geographic (JIB 2 and JIB 3), defences, ports and beaches (JIB 4), airfields (JIB 5), key points (JIB 6), oil (JIB 7) and telecommunications (JIB 8).

When the Ministry of Defence (MOD) was formed in 1964, Naval Intelligence, Military Intelligence and Air Intelligence combined to form the Defence Intelligence Staff (DIS). Although the DIS focussed initially on Cold War issues, more recently its attention has moved to support for overseas operations, to weapons of mass destruction and to international counter-terrorism activities.