A Cistercian is a member of the Cistercian Order, abbreviated as OCist or SOCist (Latin: (Sacer) Ordo Cisterciensis), a Catholic religious order of monks and nuns.

They are variously called the Bernardines, after the highly influential St. Bernard of Clairvaux (though the term is also used of the Franciscan Order in Poland and Lithuania), or the White Monks, in reference to the color of the "cuccula" or white choir robe worn by the Cistercians over their habits, -as opposed to the black cucculas worn by the Benedictine monks.

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

Over the centuries, however, education and academic pursuits came to dominate the life of their monasteries.

A reform movement seeking a simpler lifestyle started in 17th-century France at La Trappe Abbey, which led to development of the Order of Cistercians of the Strict Observance (OCSO), commonly called the Trappists.

After that the followers of the older pattern of life became known as the Cistercians of the Original Observance.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 Cîteaux and the English monk Stephen Harding, who were the first three abbots.

Bernard of Clairvaux enters the monastery in the early 1110s with 30 companions and helps the rapid proliferation of the order.

By the end of the 12th century, the order has spread throughout France and into England, Wales, Scotland, Ireland, Spain, Portugal, Italy, and Eastern Europe.The keynote of Cistercian life is a return to literal observance of the Rule of St. Benedict.

Rejecting the developments the Benedictines had undergone, the monks tried to replicate monastic life exactly as it had been in Saint Benedict's time; indeed in various points they went beyond it in austerity.

The most striking feature in the reform is the return to manual labor, especially fieldwork, a special characteristic of Cistercian life.

Cistercian architecture is considered one of the most beautiful styles of medieval architecture.

Additionally, in relation to fields such as agriculture, hydraulic engineering and metallurgy, the Cistercians become the main force of technological diffusion in medieval Europe.

The Cistercians are adversely affected in England by the Protestant Reformation, the Dissolution of the Monasteries under King Henry VIII, the French Revolution in continental Europe, and the revolutions of the 18th century, but some survive and the order recovers in the 19th century.

In 1891, certain abbeys formsa new Order called Trappists (Ordo Cisterciensium Strictioris Observantiae – OCSO), which today exists as an order distinct from the Common Observance.