Charles Hartshorne was the most influential proponent of the process conception of God in the second half of the twentieth century. While often seen as a disciple of Alfred North Whithead and Charles Sanders Peirce, Hartshorne's ideas are in many ways original and often depart significantly from those of Whitehead and Peirce. "The Unity of Being" is the only major work written by Hartshorne before coming under the influence of Whitehead and Peirce has never been accessible to the public until now. This work serves, therefore, what ideas he brought to his first readings of Whitehead and Peirce. Born in rural Pennsylvania in 1897, Charles Hartshorne became a world-class philosopher of religion whose ideas about the nature of God are still being examined and articulated today. He was an especially prolific writer in his eighth and ninth decades and was even active as a centenarian. Having published 22 books between 1922 and 1997, and in the wake of his death in 2000, Hartshorne is now becoming understood as one of the few philosophers whose work bridges theology and academic philosophy. Following his teacher, Harvard professor Alfred North Whitehead, Hartshorne's distinctive contribution was to combine Whitehead's process metaphysics with theology to into a conception of God not as a static entity but as a dynamic process. Traditionally, God is seen as an unchanging, perfect being. But Hartshorne showed that God can be understood better as "always" becoming, changing, and growing in ways that can be rationally understood. Hartshorne's distinctive work has also been credited with recovering and improving St. Anselm's traditional 'ontological argument' and for reviving a version of natural theology in which God's nature and existence cannot be understood apart from the world of nature. Randall Auxier and Hyatt Carter have carefully edited and reconstructed Hartshorne's Harvard Ph.D. dissertation of the same title. "The Unity of Being" will add an important piece to Hartshorne's intellectual legacy. "The Unity of Being" will provide historians with insight into the origin of Hartshorne's ideas and the trajectory of his career, and help better illuminate Hartshorne's relationships to Whitehead and other important influences in his career, notably the American philosopher Charles Sanders Peirce.