Henotheism is the worship of a single, supreme god that does not deny the existence or possible existence of other deities that may be worshipped. Friedrich Schelling (1775–1854) coined the word, and Friedrich Welcker (1784–1868) used it to depict primitive monotheism among ancient Greeks.

Max Müller (1823–1900), a British philologist and orientalist, brought the term into wider usage in his scholarship on the Indian religions, particularly Hinduism, whose scriptures mention and praise numerous deities as if they are one ultimate unitary divine essence. Müller made the term central to his criticism of Western theological and religious exceptionalism (relative to Eastern religions), focusing on a cultural dogma which held "monotheism" to be both fundamentally well-defined and inherently superior to differing concepts of God.

Friedrich Schelling coined the German term Henotheismus from Greek ἕν (hén) 'one' and German Theismus 'theism' (which comes from Greek θεός (theós) 'god'). The term refers to a form of theism focused on a single god. Related terms are monolatry and kathenotheism. The latter term is an extension of "henotheism", from καθ' ἕνα θεόν (kath' hena theon) '"one god at a time"'. Henotheism refers to a pluralistic theology wherein different deities are viewed to be of a unitary, equivalent divine essence. Another term related to henotheism is "equitheism", referring to the belief that all gods are equal. Furthermore, the term henotheism does not exclude monism, nondualism, or dualism.

Various scholars prefer the term monolatry to henotheism, to discuss religions where a single god is central, but the existence or the position of other gods is not denied. According to Christoph Elsas, henotheism in modern usage connotes a syncretic stage in the development of religions in late antiquity. A henotheist may worship a single god from a pantheon of deities at a given time, depending on his or her choice, while accepting other deities and concepts of god. Henotheism and inclusive monotheism are terms that refer to a middle position between unlimited polytheism and exclusive monotheism.

Zoroastrianism is often regarded as one of the oldest monotheistic religions in the world. Although Ahura Mazda is the supreme god, Zoroastrianism believes in lesser divinities known as Yazatas. These yazatas ("good agents") include Anahita, Sraosha, Mithra, Rashnu, and Tishtrya. According to some scholars, there are two issues that have long made it problematic to identify Zoroastrianism as true monotheism: the presence of lesser deities and dualism. But before hastening to conclude that the Amesha Spentas and the other yazatas compromise the purity of monotheism, we should consider that the other historical monotheisms too made room for other figures endowed with supernatural powers to bridge the gulf between the exalted, remote Creator God and the human world: the angels in all of them (whose conception in post-exilic Judaism was apparently developed after the pattern of the Amesha Spentas; Boyce and Grenet, 1991, 404–405), the saints and the Virgin Mary in several Christian churches, and the other persons of the Trinity in all of Christianity. Despite the vast differences with Zoroastrian theology, the common thread is that all these beings are subordinate to the Godhead as helpers or (in the case of the persons of the Trinity) co-equals, hence they do not pursue different interests and are worshiped jointly with the Godhead, not separately; therefore the supplicant's dilemma does not arise. Others such as Richard Foltz has put forth evidence that Iranians of Pre-Islamic era worshipped all these figures, especially Mithra and Anahita.

Prods Oktor Skjærvø states Zoroastrianism is henotheistic, and "a dualistic and polytheistic religion, but with one supreme god, who is the father of the ordered cosmos". Other scholars state that this is unclear, because historic texts present a conflicting picture, ranging from Zoroastrianism's belief in "one god, two gods, or a best god henotheism".

To what is One

They call him Indra, Mitra, Varuna, Agni,
and he is heavenly-winged Garutman.
To what is One, sages give many a title.