Three recent discussions of Irenaeus by Reynders, Audet, and Enslin have examined the thought of Irenaeus almost exclusively in relation to the Christian tradition. This attitude toward his writings is natural, since Irenaeus lives so largely within the tradition; but he lived in the philosophical-rhetorical world of his day as well as in the church. It is the purpose of this paper to examine some of the ideas which he shares with non-Christians of the second century. First we shall consider his use of doxographical materials for the opinions of philosophers, and then we shall turn to his knowledge of other authors and of rhetoric.