This book is the outcome of a request to write an article on atheism for a projected dictionary of the religious history of classical antiquity. While doing research, the author decided this subject might well deserve a more comprehensive treatment and this is what he attempts to do. Contents: conception and treatment of denial of the gods in antiquity, accounts of deniers; naive criticism of popular religion, Xenophanes; ionic naturalism, Diagoras; Sophistic and his influence; Socrates and the Socratics; hellenism; period of the Roman Empire; Middle Ages and recent times; retrospect.