Monotheism (from Greek μόνος, monos, "single", and θεός, theos, "god") is the belief in the existence of one god or in the oneness of God.. Monotheism is characteristic of the Abrahamic religions (Judaism, most denominations of Christianity, Islam, Sabianism) and also recognizable in numerous other religions such as Zoroastrianism, Bahá'í Faith, Sikhism and even Hinduism.

The word monotheism is derived from the Greek μόνος (monos) meaning "single" and θεός (theos) meaning "god". The English term was first used by Henry More (1614–1687).

Some writers such as Karen Armstrong believe that the concept of monotheism sees a gradual development out of notions of henotheism (worshiping a single god while accepting the existence or possible existence of other deities) and monolatrism (the recognition of the existence of many gods, but with the consistent worship of only one deity).^{[citation needed][dubious – discuss]} However, the historical incidences of monotheism are so rare, that it's difficult to support any theory of the natural progression of religions from polytheism to henotheism to monotheism.^{[citation needed]}