Theodosius and Saint Ambrose is a painting by Peter Paul Rubens, with assistance from his main pupil Anthony van Dyck, executed c. 1615–1616. It is now in the Kunsthistorisches Museum in Vienna. Rubens created the preparatory drawing, with the painting almost entirely done by van Dyck, who painted his own similar version of the subject a few years later. In the Rubens version, the architectural background is less defined, Theodosius is bearded and the spear and halberd in van Dyck's own version are omitted.