 Process theism typically refers to a family of theological ideas originating in, inspired by, or in agreement with the metaphysical orientation of the English philosopher-mathematician Alfred North Whitehead (1861–1947) and the American philosopher-ornithologist Charles Hartshorne (1897–2000). For both Whitehead and Hartshorne, it is an essential attribute of God to be fully involved in and affected by temporal processes. This idea contrasts neatly with traditional forms of theism that hold God to be or at least conceived as being, in all respects non-temporal (eternal), unchanging (immutable,) and unaffected by the world (impassible). Process theism does not deny that God is in some respects eternal, immutable, and impassible, but it contradicts the classical view by insisting that God is in some respects temporal, mutable, and passible. The views of Whitehead and Hartshorne should also be distinguished from those that affirm that the divine being, by an act of self-limitation, opens itself to influence from the world. Some neo-Thomists hold this view and a group of Evangelical Christian philosophers, calling themselves “open theists,” promote similar ideas. These forms of theism were influenced by process theism, but they deny its claim that God is essentially in a give-and-take relationship with the world. Moreover, process theism is a genuinely philosophical theology in the sense that it is not grounded in claims of special insight or revealed truth but in philosophical reflection. Specifically, process theism is a product of theorizing that takes the categories of becoming, change, and time as foundational for metaphysics. The metaphysical underpinning of process theism is often called process philosophy, a label suggested by the title of Whitehead’s magnum opus, Process and Reality. In order to bring out this philosophy’s emphasis on relatedness, many scholars follow Bernard Loomer in calling it process-relational philosophy. Whitehead’s preferred expression for his metaphysical viewpoint is “the philosophy of organism.” This article concerns primarily the concept of God in process theism, although we shall conclude with a brief discussion of arguments for the existence of God in process thought.