Atheism, in the broadest sense, is an absence of belief in the existence of deities. Less broadly, atheism is a rejection of the belief that any deities exist. In an even narrower sense, atheism is specifically the position that there are no deities. Atheism is contrasted with theism, which in its most general form is the belief that at least one deity exists.
Historically, evidence of atheistic viewpoints can be traced back to classical antiquity and early Indian philosophy. In the Western world, atheism declined as Christianity gained prominence. The 16th century and the Age of Enlightenment marked the resurgence of atheistic thought in Europe. Atheism achieved a significant position in the 20th century with legislation protecting freedom of thought.