Atheistic existentialism is a kind of existentialism which strongly diverged from the Christian existential works of Søren Kierkegaard and developed within the context of an atheistic world view. The philosophies of Søren Kierkegaard and Friedrich Nietzsche provided existentialism's theoretical foundation in the 19th century, although their differing views on religion proved essential to the development of alternate types of existentialism. Atheistic existentialism was formally recognized after the 1943 publication of Being and Nothingness by Jean-Paul Sartre and Sartre later explicitly alluded to it in Existentialism is a Humanism in 1946. Source: Wikipedia (en)