‘Atheism in history’ is concerned with two specific questions that need to be answered as part of the wider argument for atheism. The first is when and why atheism emerged in Western history. Atheism had its origins in the naturalism of the pre-Socratic Milesian philosophers of Ancient Greece, but did not emerge as an overt and avowed belief system until late in the Enlightenment. The second question concerns the extent to which atheism is implicated in the terrors of 20th-century totalitarianism in the Soviet Union, Nazi Germany, Italy, and Spain. The answer to the first strengthens the case for atheism, while an answer to the second weakens some objections to it.