The Son Tay Campaign (11 December 1883 to 17 December 1883) was a campaign fought by the French to capture the strategically important city of Son Tay in Tonkin (northern Vietnam) from Liu Yongfu's Black Flag Army and allied contingents of Vietnamese and Chinese troops. The campaign was one of several clashes between the Tonkin Expeditionary Corps and the Black Flag Army during the Tonkin Campaign (1883–1886), and took place during the period of undeclared hostilities that preceded the Sino-French War (August 1884–April 1885).