The 66th Battalion, CEF was an infantry battalion of the Canadian Expeditionary Force during the First World War. The battalion was authorized on 20 April 1915 and embarked for Britain on 28 April 1916. Its personnel were absorbed by the 9th Reserve Battalion, CEF on 7 July 1916 to provide reinforcements for the Canadian Corps in the field. The battalion was disbanded on 30 August 1920.