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