Philo of Alexandria, a first century Jewish philosopher, appears as the first thinker who tried to conciliate biblical contents and western philosophical tradition. In this way, he is better known by his Doctrine of the Logos, about which many controversies are still waiting to be solved. This Dissertation claims the task to examine the meanings of that Logos in Philos works, dealing with its connections to philosophical tradition and Jewish sources as well. We pay regard to its significance to Christian theology and to the role played by philosophical tradition, especially by Platonism as by Stoicism. Otherwise, the Philos thinking still shows itself original and marked by contributions external to the hellenistic culture: Jewish ones. This combination has, by result, provocative ideas on most important metaphysical, theological, ethical and epistemological questions, revealing Philo as a very weighty thinker in the History of Philosophy. For this, the Dissertation aims to restore many questions that we see not yet properly answered. Also questioned are the role played by philosophy in the human search for wisdom and the role played by faith in the attainment of virtue. More strictly concerning philonic Logos, it means Gods action in the world, an instrument for Creation, pattern and example for the world and Gods image, the revealing Word and the sole way by which human soul acquires true knowledge, that comes from the knowledge of God. This power does not belongs to man, but its a gift from God, a grace.