Marsh, Adam, or Adam de Marisco, d. 1259?, English Franciscan scholar. He was a student of Robert Grosseteste. When Grosseteste became bishop, Marsh took his place in the Franciscan school at Oxford. Marsh's advice and his services as a peacemaker were constantly sought, and Grosseteste relied heavily on him. Actively supporting the reform party of Simon de Montfort (1208?-1265), Marsh was able nevertheless to retain the confidence of Henry III. Of his writings only his letters survive.