Charles-François Toustain (born at Repas in the diocese of Séez, France, 13 October 1700, died at Saint-Denis, 1 July 1754) was a French historian and Benedictine, member of the Congregation of St-Maur.
He belonged to a family of note. On 20 July 1718, he made the vows of the order at Jumièges. After finishing the philosophical and theological course at the Abbey of Fécamp, he was sent to the monastery of Bonne-Nouvelle at Rouen, to learn Hebrew and Greek. At the same time he studied Italian, English, German, and Dutch, in order to be able to understand the writers in these languages.
He was not ordained priest until 1729 and then only at the express command of his superior. He always said Mass with much trepidation and only after long preparation. In 1730 he entered the Abbey of St-Ouen at Rouen, went later to the Abbey of St-Germain-des-Pres and Blancs-Manteaux, and died while taking his milk-cure at Saint-Denis. He had worn out his body by fasting and ascetic practices.
His theological opinions inclined to Jansenism. As a scholar he made himself an honoured name. He worked for twenty years with a fellow-member of the order, Dom Tassin, on an edition of the works of St. Theodore of Studium. It was never printed, for a publisher could not be found. Another common undertaking of the two is the "Nouveau traité de diplomatique" (6 vols., 1750–65) in which they treated more fully and thoroughly the subjects taken up in Mabillon's great work "De re diplomatica". The publication of Toustain and Tassin is of permanent value. The last four volumes were edited by Tassin alone after Toustain's death.
Of general interest among Toustain's personal writings are: "La vérité persécutée par l'erreur" (2 vols., 1733), a collection of the writings of the Fathers on the persecutions of the first eight centuries; and "L'authorité de miracles dans l'Église" (no date), in which he expounds the opinion of St. Augustine. Tassin testifies that he was zealous in his duties, modest, and sincerely religious.