Monotheism: the word indicates a system of thought that proceeds from a recognition of the divinity of a single god to the exclusion of all other. This exclusivity distinguishes monotheism from henotheism or monolatry and explains why monotheism is a question of belief, unlike traditional eastern religions, among them the religion of the Old Testament. The paper shows that monotheism is in fact absent from the Hebrew Bible by examining in particular the Creation stories and the vocabulary of divine oneness. It is in the Roman period, particularly in Philo of Alexandria's work, that we find more properly monotheistic writing, influenced by exegesis based on cosmogonic myths, foremost among them the biblical story known as the Creation. Imperial power would have had to assume a truly universal character for the idea of a single god assuring that power to emerge from the multitude.