Existentialism emphasizes concrete human existence, freedom of choice, and responsibility for one's actions. Key existentialist philosophers include Kierkegaard, Nietzsche, Heidegger, Sartre, and Camus. They addressed themes like anxiety, authenticity, absurdity, and the need to define one's own purpose and values rather than rely on external rules. Literature exploring these themes includes works by Dostoevsky, Kafka, Hesse, and Camus that depict individuals grappling with the lack of inherent meaning in an indifferent world.