Dom Didier de La Cour de La Vallée (1550 – 1623) was a Benedictine monk, responsible for the foundation of the reforming Congregation of St. Vanne in 1604.
Dom Didier was born at Montzéville, Meuse, in December 1550, into an ancient noble family of Lorraine but one which had grown so poor that they were obliged to work on their own lands. At 18, he entered St. Vanne's Abbey in Verdun and later studied at the University of Pont-à-Mousson, where he became friendly with Servais de Lairuelz and Saint Pierre Fourier.
He returned to Verdun fired with the desire to reform monastic life, but came up against the hostility of the other monks. His aim was to apply in his monastery, of which he became prior, the Rule of St. Benedict in its original rigour. Despite the initial difficulties, his efforts ultimately met with success. In 1604, the Congregation of St. Vanne was formed, which brought together all the reformist monasteries of Lorraine. By the time of Dom Didier's death in 1623, the congregation contained forty monasteries in three provinces, and had inspired the formation in France of the parallel reform movement of the Congregation of St. Maur.