In the most common usage, lay brothers are those members of Catholic religious orders occupied primarily with manual labor and with the secular affairs of a monastery or friary. They have been known, in various places and at various times, as fratres conversi, laici barbati, illiterati, or idiotæ, and, though members of their respective orders, are entirely distinct from the choir monks, who are devoted mainly to the Opus Dei ("The Work of God") and to study.
There is some dispute as to the origin of lay brothers. They are first heard of in the 11th century, and are stated by Mabillon to have been first instituted by St. John Gualbert at Vallombrosa, about 1038. The term conversi is first applied to religious of this kind in a biography of that founder, written by Bl. Andrea Strumensis about the end of the 11th century. It seems certain, however, that they were instituted before the founding of Vallombrosa. Among the Camaldolese, St. Peter Damian indicates that servants, who were also religious, were set apart to perform the manual labour at Fonte Avellana, which was founded about the year 1000. Likewise, at the Sacro Eremo at Camaldoli, founded about twenty years later, there were certainly brethren who were distinct from the hermits, and who were devoted entirely to the secular needs of the community.
No such distinction existed in early Western monasticism. The majority of St. Benedict's monks were not clerics, and all performed manual labor, the word conversi being used only to designate those who had received the habit late in life, to distinguish them from the oblati and nutriti. But, by the beginning of the 11th century, the time devoted to study had greatly increased, thus a larger proportion of the monks were in Holy Orders, even though great numbers of illiterate persons had embraced the religious life. At the same time, it was found necessary to regulate the position of the famuli, the hired servants of the monastery, and to include some of these in the monastic family. So in Italy the lay brothers were instituted; and we find similar attempts at organization at the Abbey of St. Benignus at Dijon, under William of Dijon (d. 1031) and Richard of Verdun (d. 1046), while at Hirschau, Abbot William (d. 1091) gave a special rule to the fratres barbati and exteriores. At Cluny the manual work was relegated mostly to paid servants, but the Carthusians, the Cistercians, the Order of Grandmont, and most subsequent religious orders possessed lay brothers, to whom they committed their secular cares. At Grandmont, indeed, the complete control of the order's property by the lay brothers led to serious disturbances, and finally to the ruin of the order; but the wiser regulations of the Cistercians provided against this danger and have formed the model for the later orders. In England, the "Black Monks" (Benedictines) were reported by some writers to have made but slight use of lay brothers, finding the service of paid attendants more convenient. Thus Father Taunton asserted that, "in those days in English Benedictine monasteries there were no lay brothers." On the contrary, however, they are mentioned in the customaries of the Abbey of St. Augustine at Canterbury and the Abbey of St. Peter at Westminster.
Lay brothers are often pious and hard working persons, usually drawn from the working classes of the community, who, while unable to attain to the degree of learning requisite for Holy Orders, are still drawn to the religious life and are able to contribute to their house or order. They primarily perform perform domestic or agricultural work, are often skilled in artistic handicrafts, and they sometimes are efficient administrators. For example, the lay brethren of the Cistercians are thought to be a significant source of the order's success in agriculture in modern as well as in medieval times.
Lay brothers are usually distinguished from their brethren by some difference in their habit: for instance, the Cistercian lay brother wears a brown tunic, instead of white, with the black scapular; in choir they wear a large cloak, instead of a cowl; the Vallombrosan lay brothers wore a cap instead of a hood, and their habit was shorter; the English Benedictine lay brothers wear a hood of a different shape from that of the choir monks, and no cowl; a Dominican lay brother wears a black, instead of a white, scapular. In some orders they are required to recite daily the Little Office of Our Lady, but usually their office consists of a certain number of Paters, Aves, and Glorias. Wherever they are found in considerable numbers they possess their own quarters in the monastery; the domus conversorum is still noticeable in many of the ruins of English monasteries.
Lay sisters are to be found in most of the orders of women, and their origin, like that of the lay brothers, is to be found in the necessity at once of providing the choir nuns with more time for the Office and study, and of enabling the unlearned to embrace the religious life. They, too, are distinguished by their different habit from the choir sisters, and their Office consists of the Little Office of Our Lady or a certain number of Paters, etc. They seem to have been instituted earlier than the lay brothers, being first mentioned in a life of St. Denis written in the 9th century. In the early medieval period we even hear of lay brothers attached to convents of women and of lay sisters attached to monasteries. In each case, of course the two sexes occupied distinct buildings. This curious arrangement has long been abolished.
Among the various teaching orders, the majority of male communities are comprised solely of laymen, and are thus considered lay brothers, in the more general sense of the word. While they are not clergy, unlike those in this category in the monastic life, most are highly trained and professional individuals, not uncommonly having doctoral degrees.
The changes brought about the Second Vatican Council included the call to all religious orders to re-examine and renew their origins. As a result, most of the distinctions noted above, in terms of dress and spiritual regimen were abolished or mitigated. While some continue to be known as Brothers, all members of a religious order now have equal rights and wear the same habit.