Existentialism is a movement in philosophy and literature that emphasizes individual existence, freedom and choice. It began in the mid-to-late 19th Century, but reached its peak in mid-20th Century France. It is based on the view that humans define their own meaning in life, and try to make rational decisions despite existing in an irrational universe. It focuses on the question of human existence, and the feeling that there is no purpose or explanation at the core of existence. It holds that, as there is no God or any other transcendent force, the only way to counter this nothingness (and hence to find meaning in life) is by embracing existence.

Thus, Existentialism believes that individuals are entirely free and must take personal responsibility for themselves (although with this responsibility comes angst, a profound anguish or dread), and emphasizes action, freedom and decision as fundamental in rising above the essentially absurd condition of humanity (which is characterized by suffering and inevitable death). For more details, see the section on the doctrine of Existentialism.

Existentialists refuse to belong to any school of thought, repudiating of the adequacy of any body of beliefs or systems, claiming them to be superficial, academic and remote from life. It is a reaction against traditional schools of philosophy, such as Rationalism, British Empiricism and Positivism, that seek to discover an ultimate order and universal meaning in metaphysical principles or in the structure of the observed world.

Existentialism in its currently recognizable form was developed by the 19th Century Danish philosopher Søren Kierkegaard and the German philosopher Friedrich Nietzsche, although neither actually used the term in their work. The Phenomenology of Martin Heidegger was another important influence on the later development of the movement. It can be argued that