The 4th Brigade is a brigade-level formation of the Australian Army. Originally formed in 1912 as a Militia formation, the brigade was re-raised for service during World War I, elements of the brigade served at Gallipoli and in the trenches on the Western Front before being disbanded in 1919. In 1921, the brigade was re-raised as a unit of Australia's part-time military forces, based in the state of Victoria. During World War II the brigade served in the New Guinea and New Britain campaigns. Following the war, the brigade formed part of the 3rd Division, however, it was later reallocated to the 2nd Division, where it serves as a Reserve combined-arms formation including units and personnel from all corps of the Army including armoured, infantry, artillery, engineers, signals and ordnance.

The Australian Army Reserve is a collective name given to the reserve units of the Australian Army. Since the Federation of Australia in 1901, the reserve military force has been known by many names, including the Citizens Forces, the Citizen Military Forces, the Militia and, unofficially, the Australian Military Forces. In 1980, however, the current name—Australian Army Reserve—was officially adopted, and it now consists of a number of components based around the level of commitment and training obligation that its members are required to meet.