Augustinian nuns are the most ancient and continuous segment of the Roman Catholic Augustinian religious order under the canons of contemporary historical method. The Augustinian nuns, named after Saint Augustine of Hippo, are several Roman Catholic enclosed monastic communities of women living according to a guide to religious life known as the Rule of St. Augustine. Prominent Augustinian nuns include Italian mystic St. Clare of Montefalco and St. Rita of Cascia.

Augustinians are members of several religious orders that follow the Rule of Saint Augustine, written in about 400 AD by Augustine of Hippo. There are two distinct types of Augustinians in Catholic religious orders dating back to the 12th–13th centuries:Various congregations of Canons Regular also follow the Rule of Saint Augustine, embrace the evangelical counsels and lead a semi-monastic life, while remaining committed to pastoral care appropriate to their primary vocation as priests. They generally form one large community which might serve parishes in the vicinity, and are organized into autonomous congregations. Several orders of friars who live a mixed religious life of contemplation and apostolic ministry. The largest and most familiar is the Order of Saint Augustine (OSA), founded in 1244 and originally known as the Hermits of Saint Augustine (OESA). They are commonly known as the Austin Friars in England. Two other orders, the Order of Augustinian Recollects and the Discalced Augustinians, were once part of the OSA under a single prior general. The Recollects, founded in 1588 as a reform movement in Spain, became autonomous in 1612. The Discalceds became an independent congregation in 1592, and were raised to the status of a separate mendicant order in 1610.