In theology, the doctrine of divine simplicity says that God is without parts. The general idea of divine simplicity can be stated in this way: the being of God is identical to the "attributes" of God. In other words, such characteristics as omnipresence, goodness, truth, eternity, etc. are identical to God's being, not qualities that make up that being, nor abstract entities inhering in God as in a substance. Varieties of the doctrine may be found in Jewish, Christian, and Muslim philosophical theologians, especially during the heyday of scholasticism, though the doctrine's origins may be traced back to ancient Greek thought.

In classical Christian theism, God is simple, not composite, not made up of thing upon thing. In other words, the characteristics of God are not parts of God that together make up God. Because God is simple, God is those characteristics; for example, God does not have goodness, but simply is goodness. For typical Christian theologians, divine simplicity does not entail that the attributes of God are indistinguishable to thought. It is no contradiction of the doctrine to say, for example, that God is both just and merciful. Thomas Aquinas, for instance, in whose system of thought the idea of divine simplicity is central, wrote in Summa Theologica that because God is infinitely simple, God can only appear to the finite mind as infinitely complex.^{[citation needed]}