With its emphasis on individuality, freedom, and personal responsibility, existentialism was one of the 20th century's most significant philosophical movements. Through such writers as Sarte, de Beauvoir, and Camus, it influenced literature, the arts and humanities, and politics. Thomas R. Flynn examines the philosophy's core beliefs, focusing on several key existential themes, and introduces the leading existentialist thinkers, from Kierkegaard and Nietzsche to Sartre.