The Canons Regular of St. Augustine are Catholic priests who live in community under a rule (Latin: regula and κανών, kanon, in Greek) and are generally organised into religious orders, differing from both secular canons and other forms of religious life, such as clerics regular, designated by a partly similar terminology. As religious communities, they have laybrothers as part of the community.

At times, their Orders have been very popular: in England in the 12th century, there were more houses of canons (often referred to as an abbey or canonry) than monasteries of monks.

All canons regular are to be distinguished from secular canons who belong to a resident group of priests but who do not take public vows and are not governed in whatever elements of life they lead in common by a historical rule. One obvious place where such groups of priests are required is at a cathedral, where there were many Masses to celebrate and the Divine Office to be prayed together in community. Other groups were established at other churches which at some period in their history had been considered major churches, and (often thanks to particular benefactions) also in smaller centres.

As a norm, canons regular live together in communities that take public vows. Their early communities took vows of common property and stability. As a later development, they now usually take the three public vows of chastity, poverty and obedience, although some orders or congregations of canons regular have retained the vow of stability.

By 1125 hundreds of communities of canons had sprung up in Western Europe. Usually, they were quite independent of one another and varied in their ministries. For example, the Arrouaisians had restrained lifestyles along Cistercian lines, while the Premonstratensians were more austere.

Especially from the 11th century, among the canons regular, various groupings called congregations were formed, which partly resembled religious orders in the general modern sense. This movement parallelled in some respects the kind of bonds established between houses of monks. Among these congregations of canons regular, most adopted the Rule of St. Augustine, hence taking their name from St. Augustine, the great Doctor of the Church, "for he realized in an ideal way the common life of the Clergy". They became known as Augustinian Canons, and sometimes in English as Austin Canons (Austin being a form of Augustine). Where it was the case, they have also been known as Black Canons, from their black habits. There have always been canons regular who have not adopted the Rule of St. Augustine: all Augustinian Canons are canons regular, but not all canons regular are Augustinian Canons.

In Latin, terms such as Canonici Regulares Ordinis S. Augustini (Canons Regular of the Order of St. Augustine) were used, whereby the term order (Latin ordo) referred more to a form of life or a stratum of society, reminiscent of the usage of the equestrian order or senatorial order of Roman society, rather than to a religious order in the modern sense of a closely organized body. Furthermore, among the Augustinian Canons, some groups acquired a greater degree of distinctiveness in their style of life and organization, to the point of being in law or in effect autonomous religious orders. Examples include the Premonstratensian or Norbertine Order, sometimes known in English as White Canons, from their white habits. Yet another such order is that of the Crosiers. Encouraged by the general policies of the Holy See, especially from the late nineteenth century, some of these separate orders and congregations of Augustinian Canons have subsequently combined in some form of federation or confederation.

All the different varieties of canons regular are to be distinguished not only from secular canons but also from: