The Sisters of Charity of Montreal, formerly called The Sisters of Charity of the Hôpital Général of Montreal and more commonly known as the Grey Nuns of Montreal, is a Canadian religious institute of Roman Catholic religious sisters, founded in 1737 by Marie-Marguerite d'Youville, a young widow.

The congregation was founded when Marguerite d'Youville and three of her friends formed a religious association to care for the poor. They rented a small house in Montreal on 30 October 1738, taking in a small number of destitute persons. On 3 June 1753 the society received a royal sanction, which also transferred to them the rights and privileges previously granted by letters patent in 1694 to the Frères Hospitaliers de la Croix et de Saint-Joseph (French for 'Hospitaller Brothers of the Cross and of Saint Joseph'), known after their founder as the Frères Charon. At that time they also took over the work of the bankrupt Frères Charon at the Hôpital Général de Montréal ('Montreal General Hospital') located outside the city walls. (In the seventeenth century, a general hospital was an institution that took in old people, the ill, and the poor. Medical care was dispensed at the Hôtel-Dieu.)

In 1755 the sisters cared for those stricken during a smallpox epidemic. As the sisters were not cloistered, they could go out to visit the sick. Those assisted included the First Nations people in Oka, who were among the benefactors who later helped rebuild the hospital after a fire in 1765.

After 1840 the order rapidly expanded, and over the next 100 years became a major provider of health care and other social services throughout Quebec, Western and Northern Canada, and the northern United States. In 1855, the Grey Nuns were called to Toledo, Ohio, to care for many suffering from cholera. St. Vincent's later became part of Catholic Health Partners.

St. Joseph Hospital was founded in 1906 in Nashua, New Hampshire, by the parish of St. Louis de Gonzague primarily to serve Nashua's French Canadian community. The Grey Nuns began to staff it in 1907. The hospital was dedicated on 1 May 1908, the Feast of St. Joseph the Worker. The sisters also started a nursing school. In 1938, the parish transferred ownership to the sisters.

In 1983 the Grey Nuns established Covenant Health Systems, a non-profit Catholic regional health care system, to direct, support and conduct their health care, elder care and social service systems throughout New England. In 1996, sponsorship of St. Joseph Hospital in Nashua was transferred from the sisters to Covenant Health Systems.

The Grey Nuns worked as nurses and teachers in a number of Indian residential schools, as the preferred missionary partners of the Missionary Oblates of Mary Immaculate, who were not allowed to teach girls. The Oblates paid parents to allow their children to attend boarding schools. At the schools, they participated in the effort to remove children from their traditional Indigenous ways of life, in order to "civilize" them.

The main goal of the Oblates and the Grey Nuns was to provide a Catholic education (in competition with schools operated by Anglicans) and to give a limited secular education. These early mission boarding schools never recruited more than a small percentage of the school-aged children in the region. Though often at odds, the Canadian government and the various religious organizations operating residential schools agreed that Indigenous cultural practices had to be suppressed.