This document provides an overview of existentialism and some of its key philosophers. It discusses how existentialism emphasizes individual existence, freedom and choice. Existentialists believe humans define their own meaning in life and make rational decisions despite living in an irrational universe. The document profiles philosophers like Kierkegaard, Nietzsche and Sartre, noting their views on topics like how existence precedes essence, the absurdity of life, and humans' condemned freedom. It also briefly discusses nihilism and how existentialism differs by asserting one can overcome the absurdity of existence.