The Order of Cistercians ( /sɪˈstɜrʃⁱən/;OCist. Latin: Ordo Cisterciensis or, alternatively, OCSO for the Trappists (Order of Cistercians of the Strict Observance)) is a Roman 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.

The term Cistercian (French Cistercien), derives from Cistercium, the Latin name for the village of Cîteaux, near Dijon in eastern France. It was in this village that a group of Benedictine monks from the monastery of Molesme founded Cîteaux Abbey in 1098, with the goal of following more closely the Rule of Saint Benedict. The best known of them were Robert of Molesme, Alberic of Citeaux and the English monk Stephen Harding, who were the first three abbots. Bernard of Clairvaux entered the monastery in the early 1110s with 30 companions and helped the rapid proliferation of the order. By the end of the 12th century, the order had spread throughout France and into England, Wales, Scotland, Ireland, Spain, Portugal, Italy, and Eastern Europe.