This study examines the theology of St. John of Damascus on images in the context of the Byzantine iconoclastic controversies. Following a brief outline of the historical, political and theological difficulties relevant to this phenomenon, the Christological and ontological dimensions of John's iconology are presented. John's iconological thought is Christ-centered and develops the teaching of the Church on Christ's person and two natures. He formulates an iconological realism based on the Incarnation. This study also analyzes the role of matter as charged with divine energy and grace, the function of the icon as symbol, and the development of a cognitive theory in John's treatises on images. Lastly, John's theology regarding the sixth kind of image, namely the natural icon, is contextualized within the metaphysical/cosmological chain of images he constructs. This contributes an ontological dimension to his theological discourse and grounds its fundamental importance for Christian faith, which he viewed as threatened by the conflict under discussion.