The present work tries to approach Agustine's doctrine of illumination, from a critica] reading of his De Magistro. The doctrine of illumination is the center of Agustine's philosophical thought. That doctrine would be the common ground in which Agustine's ontologic and gnoseologic thought is concentrated. It represents Agustine's answer to the ontologic question on what things are and the gnoseologic question on how do we get to know things. In De Magistro, the answer to the fundamental (onto- noseologic) questions, acquires the forro a thoughtful, dialogic, ascending and progressive a way: It is possible to see that the course of thought that is followed by Agustine is based on a platonic ontologic structure made up of two components: the internal and the external, the upper and the lower. It is from the ascending structure of the writing that this paper takes the structure for its two main sections: first, on the relation between language and things, and second, on the doctrine of the illumination: the knowledge of things themselves. At the end of the work a third section has been added, in which some of the most meaningful repercussions are developed: the influence exerted by the doctrine of the illumination in later philosophers of the middle ages and, also, the pertinent conclusions.