Philosophies that involve living without theistic beliefs can be found in many cultures. In the East, living a contemplative life without gods began with Lao Zi who wrote of the Tao (the Way), and Siddhartha Gautama, the Buddha in the 6th century BCE, founder of Buddhism. These worldviews are considered major religions, however, the original doctrinal texts do not advocate or describe deities, or related deity-worship. While later enthusiasts introduced deities and deity-worship, the practical application of these worldviews to religious thought remains atheistic. In the West, theism was the fundamental belief that supported the divine right of the State. Historically, any person who did not believe in any deity supported by the State was fair game to accusations of atheism, a capital crime. For political reasons, Socrates in Athens (399 BCE) was accused of being 'atheos' ("refusing to acknowledge the gods recognized by the state"). Despite the charges, he claimed inspiration from a divine voice and on his deathbed he asked that a rooster be sacrificed to the god Asclepius. Christians in Rome were also considered subversive to the state religion and prosecuted as atheists. Thus, charges of atheism, meaning the subversion of religion, were often used similarly to charges of heresy and impiety — as a political tool to eliminate diversity in religion.

The term atheisme itself was coined in France in the 16th century, and was initially used as an accusation against critics of religion, scientists, materialistic philosophers, deists, and others who seemed to represent a threat to established beliefs. The charge was almost invariably denied. Thus, the concept of atheism re-emerged initially as a reaction to the intellectual and religious turmoil of the Age of Enlightenment and the Reformation — as a charge used by those who saw the denial of god and godlessness in the controversial positions being put forward by others. How dangerous it was to be accused of being an atheist at this time is illustrated by the fact that in 1766, the French nobleman Jean-François de la Barre, was tortured, beheaded, and his body burned for alleged vandalism of a crucifix, a case that became celebrated because Voltaire tried unsuccessfully to have the sentence reversed.

In 1884, Karl Marx (1818–1883), an atheistic political economist, wrote in his Contribution to the Critique of Hegel's Philosophy of Right:
"Religious suffering is, at one and the same time, the expression of real suffering and a protest against real suffering. Religion is the sigh of the oppressed creature, the heart of a heartless world, and the soul of soulless conditions. It is the opium of the people.Marx believed that people turn to religion in order to dull the pain caused by the reality of social situations; that is, Marx suggests religion is an attempt at transcending the material state of affairs in a society — the pain of class oppression — by effectively creating a dream world, rendering the religious believer amenable to social control and exploitation in this world while they hope for relief and justice in life after death. In the same essay, Marx states, "...[m]an creates religion, religion does not create man..."

Friedrich Nietzsche, a prominent 19th century atheist, coined the aphorism "God is dead". Nietzsche argued that the Western belief system was a metaphysical system based on theological (Christian) foundations. With the death of God (i.e., the collapse of Christianity as a serious belief system), the whole system of Western thought crumbled, hence Nietzsche's call for a re-evaluation of all values.

Contemporary atheism
Atheism is common in Western Europe, in former or present communist states, and in the United States and Canada. It is particularly prevalent among scientists, a tendency already quite marked at the beginning of the twentieth century, developing into a dominant one during the course of the century. In 1914, James H. Leuba found that 58% of 1,000 randomly selected U.S. natural scientists expressed "disbelief or doubt in the existence of God". The same study, repeated in 1996, resulted in 93% expressing such disbelief or doubt. Expressions of positive disbelief rose from 52% to 72%.

In the United States, there is widespread disapproval of atheists. For example, according to motherjones.com, 52% of Americans claim they would not vote for a well-qualified atheist for president. Notwithstanding such attitudes, atheists are legally protected from discrimination in the United States. They have been among the strongest advocates of the legal separation of church and state. American courts have regularly, if controversially, interpreted the constitutional requirement for separation of church and state as protecting the freedoms of non-believers, as well as prohibiting the establishment of any state religion. Atheists often sum up the legal situation with the phrase: "Freedom of religion also means freedom from religion."

In the Board of Education of Kiryas Joel Village School District v. Grumet, Justice Souter ruled: "government should not prefer one religion to another, or religion to irreligion." Everson v. Board of Education established that "neither a state nor the Federal Government can... pass laws which aid one religion, aid all religions, or prefer one religion over another". This applies the Establishment Clause to the states as well as the federal government. However, several state constitutions make the protection of persons from religious discrimination conditional on their acknowledgement of the existence of a deity, apparently making freedom of religion in those states inapplicable to atheists. These state constitutional clauses have not been tested. Civil rights cases are typically brought in federal courts; so such state provisions are mainly of symbolic importance.

In the Newdow case, after a father challenged the phrase "under God" in the United States Pledge of Allegiance, the Ninth Circuit Court of Appeals found the phrase unconstitutional. Although the decision was stayed pending the outcome of an appeal, there was the prospect that the pledge would cease to be legally usable without modification in schools in the western United States, over which the Ninth Circuit has jurisdiction. This resulted in political furor, and both houses of Congress passed resolutions condemning the decision, nearly unanimously. A very large group consisting of almost the entire Senate and House was televised standing on the steps of Congress, hands over hearts, swearing the pledge and shouting out "under God". The Supreme Court subsequently reversed the decision, ruling that Michael Newdow did not have standing to bring his case, thus disposing of the case without ruling on the constitutionality of the pledge.