The 4th Light Horse Brigade was a mounted infantry brigade of the Australian Imperial Force (AIF) serving in the Middle Eastern theatre of World War I. The brigade was initially formed as a part-time militia formation in the early 1900s in Victoria and Tasmania. After the outbreak of World War I, the brigade was raised as a volunteer formation within the AIF in March 1915 and shipped to Egypt and was broken up in August 1915 to provide dismounted reinforcements to other light horse formations already deployed to Gallipoli. Reformed in February 1917, the brigade was assigned to the Imperial Mounted Division, which formed part of the Egyptian Expeditionary Force, and in June 1917 transferred to the Australian Mounted Division, where it served in the Sinai and Palestine Campaign until the end of the war. After the war, the AIF light horse regiments were demobilised and disbanded; however, the brigade briefly existed as a part-time militia formation in New South Wales until 1921 when its regiments were reorganised into cavalry brigades.

Australian Light Horse were mounted troops with characteristics of both cavalry and mounted infantry, who served in the Second Boer War and World War I. During the inter-war years, a number of regiments were raised as part of Australia's part-time military force. These units were gradually mechanised either before or during World War II, although only a small number undertook operational service during the war. A number of Australian light horse units are still in existence today.