Criticism of religion involves criticism of the validity, concept, or ideas of religion. Historical records of criticism of religion go back to at least 5th century BCE in ancient Greece, in Athens specifically, with Diagoras "the Atheist" of Melos. In ancient Rome, an early known example is Lucretius' De rerum natura from the 1st century BCE.

Deism 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, 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.