Existentialism is a form of philosophical inquiry that explores the issue of human existence. It is a philosophy of human nature that identifies people as having free will to determine the course of their lives. Existentialist philosophers explore questions related to the meaning, purpose, and value of human existence. The movement has had a profound impact on the development of humanistic and existential approaches to psychotherapy.

Existentialist philosophy encompasses a range of perspectives, but it shares certain underlying concepts. Among these, a central tenet of existentialism is that personal freedom, individual responsibility, and deliberate choice are essential to the pursuit of self-discovery and the determination of lifes meaning. Some key concepts in existentialist thought include existential crisis, dread, and anxiety in the face of an absurd world, as well as authenticity, courage, and virtue.

Existentialists are critical of our ingrained tendency to conform to the norms and expectations of the public world because it prevents us from being authentic or true to ourselves. An authentic life is one that is willing to break with tradition and social convention and courageously affirm the freedom and contingency of our condition. Existentialists generally affirm the view that the human being has free will, is able to make decisions, and can be held responsible for their actions.

The term "existentialism" was coined by the French Catholic philosopher Gabriel Marcel in the mid-1940s. The movement has had a broad and diverse range of incarnations, and it is difficult to explain what the term "existentialism" refers to. The major contributors are anything but systematic and have widely divergent views, and of these, only Sartre and Beauvoir explicitly self-identified as "existentialists".