The Mission Priests of the Immaculate Conception also called the Missionaries of Rennes were a missionary religious institute of Roman Catholic priests. The priests of the congregation are usually called Missionaries of Rennes. Founded at St-Méen in the Diocese of Rennes, by Jean-Marie de Lamennais (1780 - 1860), for the care of the diocesan seminary and the holding of missions. The disciples of the founder's younger brother, Félicité, in 1829 withdrew with him into the solitude of La Chênaie, forming the famous Society of St. Peter, with which the elder community at its own request was united, under the superiorship of Félicité.
The new congregation was placed under simple vows, the aims proposed being the defence of the Faith, the education of youth, and the giving of missions. A house of studies was erected at Malestroit, near Ploérmel, and placed under the direction of Fathers Blanc and Rohrbacher, while Lamennais remained at La Chênaie, with the younger members, writing for them his "Guide de la jeunesse", and for others more advanced the "Journée du chrétien". Lamennais's long-cherished project of forming a body of priests thoroughly equipped for pressing needs in the Church of France, a scheme which he outlined in 1825 in a letter to M. de Salinis, seemed well on the way towards fulfilment. A vivid picture of the rule of life and the spirit of La Chênaie is to be found in the letters of Maurice de Guérin, whose companions were such men as Olympe-Philippe Gerbet, Guéranger, Jean-Joseph Gaume, Scorbiac and Ch. de Sainte-Foi.
The condemnation of L'Avenir disturbed only temporarily the activity at La Chénaie. On the final defection of Félicité, however, the Bishop of Rennes transferred to Jean-Marie the superiorship of the congregation, the members of which left La Chênaie for Malestroit, laymen being now excluded. The congregation, reorganized, gained a new lease of life in 1837 and by 1861 had 200 members in 9 houses, under the mother-house at Rennes.
The institute ceased to exist with the dissociation of religious orders in France.