The Brethren of the Common Life (Latin: Fratres Vitae Communis, FVC) was a Roman Catholic pietist religious community founded in the Netherlands in the 14th century by Gerard Groote, formerly a successful and worldly educator who had had a religious experience and preached a life of simple devotion to Jesus Christ. They believed that Christianity should be practiced not only in formal religious settings, but also in everyday life, and they sought to promote a practical spirituality that emphasized personal piety and devotion.

Without taking up irrevocable vows, the Brethren or Sisters banded together in communities, giving up their worldly goods to live chaste and strictly regulated lives in common houses, devoting every waking hour to attending divine service, reading and preaching of sermons, labouring productively such as by copying manuscripts, and taking meals in common that were accompanied by the reading aloud of Scripture: "judged from the ascetic discipline and intention of this life, it had few features which distinguished it from life in a monastery", observes Hans Baron, yet still interacting with the wider community to a certain extent. The Brethren were specially involved in youth education, running or chaplaining many schools and associated hostels. Priests in a brotherhouse would become confessors for the neighbouring sisterhouse.

The Brethren of the Common Life were an important religious movement of the late Middle Ages and the Renaissance, and their emphasis on education, personal piety, and social justice had a profound influence on the religious and intellectual culture of Europe. Over time, the communities took on a more conventional monastic character as observantist canons, monks and nuns.

The four cornerstones of the Brethren were

The Confraternity of the Common Life were in many ways similar to the Beghard and Beguine communities which had flourished two centuries earlier but were by then declining. Its members took no vows and neither asked nor received alms; their first aim was to cultivate the interior life, and they worked for their daily bread.

The antifraternal insistence on work distinguishes the Brethren from mendicant (begging) friars; they were attacked by mendicant theologians at the Council of Constance for not having mainstream formal vows initially, but were successfully defended by Pierre d'Ailly and Jean Gerson.

The Brethren's confraternity is the best known fruits of the "Devotio Moderna", (the Modern Devotion), a lifestyle and undogmatic form of piety which some historians have argued helped to pave the road for the Protestant Reformation. In the fifteenth century, the movement spread to southern and western Germany. The Protestant Reformers, including Martin Luther and John Calvin, were influenced by the ideas and practices of the Devotio Moderna.

Of wealthy burgher stock, Groote was born in Deventer in the Oversticht possession of the Duchy of Guelders in 1340. Having read at Cologne, at the Sorbonne, and at Prague, he took orders and obtained preferment, a canon's stall at Utrecht and another at Aachen. His relations with the German Gottesfreunde and the writings of John of Ruusbroec, who later became his friend, gradually inclined him to mysticism, and on recovering from an illness in 1373, he resigned his prebends, bestowed his goods on the Carthusians of Arnhem and lived in solitude for seven years.