The 21st Brigade was a brigade-sized infantry unit of the Australian Army. Formed in April 1940 as part of the Second Australian Imperial Force, the unit was raised for service during World War II. As part of the 7th Division the brigade served during the Syria-Lebanon campaign, the Kokoda Track campaign, the Buna-Gona campaign, the landing at Nadzab, the Ramu Valley–Finisterre Range campaign and the Balikpapan landings. It was disbanded in 1946.