Jean-Paul Sartre's 'Existentialism is a Humanism' is a pivotal philosophical lecture delivered in 1945, later published as an essay. In this seminal work, Sartre eloquently defends existentialism against criticisms, particularly the accusation that it promotes nihilism or despair. He famously articulates the core principle that 'existence precedes essence,' asserting that individuals are born without inherent purpose and must define their own meaning through their choices and actions. Sartre emphasizes the profound freedom and terrifying responsibility each person bears for creating their own values and shaping their own being in a world devoid of pre-ordained meaning. This essential text provides a clear, accessible introduction to existentialist thought, highlighting its optimistic and humanistic dimensions.