Atheism has achieved renewed vigor in the West in recent years with a spate of bestselling books and growing membership in secularist and rationalist organizations, but what exactly is the nature of this peculiar form of non-belief? This article sets the context for the emergence of the ‘New Atheism’ with a review of the dominant theory of atheism’s dialectical and theological origins, and an examination of major historical episodes in atheistic thought. The author argues that a significant development has received (...) insufficient attention: the 19th-century split in atheism that produced two distinct streams of criticism. The first is scientific atheism, closely associated with Darwinism and Enlightenment rationalism. The second is humanistic atheism, aligned with the rise of the social sciences and pioneered by Marx and Feuerbach. The contemporary atheist movement is primarily rooted in the scientific tradition, excluding the humanistic approach on epistemological and political grounds, though emerging tensions within the movement suggest that the humanistic tradition still plays a role. The relationship between these two approaches within the movement should be a focus of future research. (shrink)