After his conversion in 1263, and following a vision on Mount Randa in 1273, Ramon Llull adopted a trinitarian view of the world. At the same time, he found his purpose in missionary activity, seeking to convert Christians, Muslims, and Jews to the Catholic faith. He also wanted to serve this purpose through his books. The trinitarian ontology that these books presuppose can be seen in his understanding of relations. Llull’s trinitarianism begins with the Augustinian tradition’s trinitarian understanding of the world. The basis of his trinitarian ontology lies in his understanding of correlatives, one of his most original contributions to the thought. Together with relative principles and the doctrine of God’s Dignities as absolute principles, these form the basis of his doctrine of Art, the art of combining elements. Trinitarian ontology also appears in his analysis of human’s relationship with God, in his dynamic definition of human being, and in the structure of the composition of human being. This article will show that trinitarian ontology is a presupposition of Ramon Llull’s vision of the world.