This treatise is the fruit of my sabbatical (from Keio University) in the U.S.A. from July 1983 to March 1985. It consists, of two parts. The first part is an introductory exposition of my academic pilgrimage from Chicago to Claremont, outlining the way in which process theology/philosophy now functions to influence American thought. The second part, being the main part, articulates the formative process of Whitehead's view of God. The primary source works for the study of his philosophical development on the idea of God are Science and the Modern World, Religion in the Making, and Process and Reality. Although they were all published within the period 1925-1929, still there are significant developments in the thoughts expressed, and these have special importance with respect to the idea of God. In this treatise I propose to summarize Whitehead's thought about God as it develops in these three books. The chapters on "Abstraction" and "God" in Science and Modern World constitute his first systematic excuftion into what he understood as metaphysics, and in these two chapters can be seen the first explicit indication in his writings that there is a place for "God" in his system. Based on the further development of his philosophical thought about God, he begins to discuss a God of religion. And in this case his chapter on "Religion ond Metaphysics" in Religion in the Making has special importance with respect to the doctrine of God. Although Whitehead does not incorporate into his philosophy any doctrines of established religious traditions, he sees in the Galilean origin of Christianity an image through which God's nature is best conceived. The image is "that of tender care that nothing be lost". The last chapter on "God and the World" in Process and Reality is therefore the most significant for the study of his thought about God. In this chapter is found his most thorough consideration of God's interaction with the physical world. He also elaborates on the nature of God, which is dipolar: "God, as well as being primordial, is also consequent. He is the beginning and the end". Thus, based on the thought of Alfred North Whitehead himself, it is possible to formulate a Christian natural theology.