Existentialism is a philosophical and literary movement that gained prominence in the mid-twentieth century. Primarily associated with the work of Jean-Paul Sartre and Parisian café society, existentialism was influenced by the earlier work of the Danish theologian Soren Kierkegaard and the German philosopher Friedrich Nietzsche. Although difficult to define, existentialism can be summarised by its emphasis on human existence over human essence, and the centrality of an individual’s freedom of choice. It is an atheist philosophy that rejects moral rules, but not responsibility. Though each individual is free, he or she must co-exist with other individuals’ freedom. According to existentialists, the only certainty in life is death, the recognition of which leads to despair. This existential anguish, however, can be transcended when an individual undertakes a project that will give his or her life meaning. Although not a political movement, existentialism’s links to social and political causes, such as the opposition of fascism, led to its widespread popularity in the 1960s.