The Order of Cistercians (Latin: Ordo Cisterciensis or, alternatively, O.C.S.O. for the Trappists [Order of Cistercians of the Strict Observance]) is a Catholic religious order of enclosed monks and nuns. They are sometimes also called the Bernardines or the White Monks, in reference to the colour of the habit, over which a black scapular is worn.

The emphasis of Cistercian life is on manual labour and self-sufficiency, and many abbeys have traditionally supported themselves through activities such as agriculture and brewing ales.