Existentialism is a European philosophy originating before the 20th century that focuses on individual experience, freedom of choice, and personal responsibility. It deals with questions about the meaning of life, identity, and the nature of reality. Existentialism believes that through free will and personal choice, individuals are responsible for creating meaning and purpose in their own lives. Key philosophers who contributed to existentialist thought include Søren Kierkegaard, Friedrich Nietzsche, Martin Heidegger, Jean-Paul Sartre, and Simone de Beauvoir.