A canoness is a member of a religious community of women, historically a stable community dedicated to the celebration of the Liturgy of the Hours in a particular church. The name corresponds to a canon, the male equivalent, and both roles share a common historical origin. As with the canons, there are two types: canonesses regular, who follow the Rule of St Augustine, and secular canonesses, who follow no monastic rule of life.

In the 21st century, the term has come to extend to women exercising the historically male role of canon in some Anglican context. Many female Anglican clerics however use the title canon and not canoness (see Male as norm), e.g., Sarah Foot.

The involvement of women in the work of the Church goes back to the earliest time, and their uniting together for community exercises was a natural development of religious worship. Many religious orders and congregations of men have related convents of nuns, following the same rules and constitutions, with many communities of canonesses taking the name and rule of life laid down for the congregations of regular canons.

Saint Basil the Great in his rules addresses both men and women. Augustine of Hippo drew up the first general rule for such communities of women. It was written in the year 423 and was addressed to Felicitas, Superioress of the Monastery of Hippo, and to Rusticus, the priest whom Augustine had appointed to have charge of the nuns. In Ireland, Saint Patrick instituted canons regular, and Saint Bridget was the first of numberless canonesses. The monasteries of the Gilbertine Order were nearly always double, for men and women.

Towards the close of the 8th century, the title of canoness is found for the first time, and it was given to these communities of women who, while they professed a common life, yet did not carry out to its full extent the original Rule of St. Augustine. These canonesses were practically an imitation of the chapters of canons regular which had then recently been received through the introduction of the Regula vitæ communis of St. Chrodegang of Metz. The canonesses took but two vows, chastity and obedience. Their superiors were known as abbesses, often held princely rank and had feudal jurisdiction.

The occupations of the canonesses consisted in the recitation of the Divine Office, the care of the church vestments, and the education of the young, particularly the daughters of the nobility. The regular canonesses, for the most part, follow the Rule of St. Augustine, but local circumstances have been the means of introducing various changes in details.

Some communities of canonesses occupied themselves in the education of children, for example the Canonesses of the Congregation of Notre Dame (French: Congrégation de Notre-Dame de chanoinesses de Saint-Augustin), instituted in 1597 at Mattaincourt, in Lorraine, by St. Peter Fourier, C.R.S.A., and the Blessed Alix Le Clerc, C.N.D. This congregation, whose charism is the education of poor girls, spread rapidly in France and Italy. In France alone, until the persecution of 1907, they had some thirty communities and as many schools for externs and boarders. Driven from France, some took refuge in England, like those of the famous convent of Les Oiseaux, Paris, who moved to Westgate-on-Sea, and those of Versailles who settled in Hull.

In many religious orders and congregations, communities of men and communities of women are related, following the same rules and constitutions. In the first centuries of the Church, the one generally began with the other. Most, if not all, of the congregations which go to form the canonical order had, or still have, a correlative congregation for women.