Deism ( DEE-iz-əm  or DAY-iz-əm; derived from the Latin deus, meaning "god") is the philosophical position and rationalistic theology that generally rejects revelation as a source of divine knowledge, and asserts that empirical reason and observation of the natural world are exclusively logical, reliable, and sufficient to determine the existence of a Supreme Being as the creator of the universe. More simply stated, Deism is the belief in the existence of God, specifically in a creator who does not intervene in the universe after creating it, solely based on rational thought without any reliance on revealed religions or religious authority. Deism emphasizes the concept of natural theology (that is, God's existence is revealed through nature).

Since the 17th century and during the Age of Enlightenment (especially in 18th-century England, France, and North America), various Western philosophers and theologians formulated a critical rejection of the several religious texts belonging to the many organized religions, and began to appeal only to truths that they felt could be established by reason as the exclusive source of divine knowledge. Such philosophers and theologians were called "Deists", and the philosophical/theological position they advocated is called "Deism".

Deism as a distinct philosophical and intellectual movement declined toward the end of the 18th century but had its own revival in the early 19th century. Some of its tenets continued as part of other intellectual and spiritual movements, like Unitarianism, and Deism continues to have advocates today, including with modern variants such as Christian deism and pandeism.