God is often conceived as the supreme being and principal object of faith. In theism, God is the creator and sustainer of the universe. In deism, God is the creator (but not the sustainer) of the universe. In pantheism, God is the universe itself. Theologians have ascribed a variety of attributes to the many different conceptions of God. Common among these are omniscience (infinite knowledge), omnipotence (unlimited power), omnipresence (present everywhere), omnibenevolence (perfect goodness), divine simplicity, and eternal and necessary existence. Monotheism is the belief in the existence of one God or in the oneness of God. God has also been conceived as being incorporeal (immaterial), a personal being, the source of all moral obligation, and the "greatest conceivable existent". Many notable medieval philosophers and modern philosophers have developed arguments for and against the existence of God.

There are many names for God, and different names are attached to different cultural ideas about who God is and what attributes he possesses. In the Hebrew Bible "I Am that I Am", and the "Tetragrammaton" YHVH are used as names of God, while Yahweh, and Jehovah are sometimes used in Christianity as vocalizations of YHVH. In Arabic, the name Allah ("the God") is used, and because of the predominance of Islam among Arab speakers, the name "Allah" has connotations with Islamic faith and culture. Muslims regard a multitude of titular names for God, while in Judaism it is common to refer to God by the titular names Elohim or Adonai. In Hinduism, Brahman is often considered a monistic deity. Other religions have names for God, for instance, Baha in the Bahá'í Faith, Waheguru in Sikhism, and Ahura Mazda in Zoroastrianism.