The Australian Department of Defence is the Australian Government's lead agency responsible for defending Australia and its national interests, protecting its people, and advancing its security and prosperity. Operating under the Minister for Defence, the Department encompasses both the civilian Australian Public Service workforce and the uniformed Australian Defence Force (ADF) — comprising the Royal Australian Navy, Australian Army, and Royal Australian Air Force — working as one integrated organisation under the overarching direction of the Chief of the Defence Force and the Secretary of the Department. The Department's responsibilities span warfighting capability, international alliances and relationships, defence industry partnerships, scientific and technological research through the Defence Science and Technology Group, and the management of Australia's substantial defence estate and infrastructure.

Operating across all domains — land, sea, air, space, and cyber — Defence maintains a force posture aligned with Australia's 2024 National Defence Strategy, deepening interoperability with key allies including the United States, the United Kingdom, and Japan through initiatives such as AUKUS and the Quad