The Penultimate Truth is a 1964 science fiction novel by American writer Philip K. Dick. The story is set in a future where the bulk of humanity is kept in large underground shelters. The people are told that World War III is being fought above them, when in reality the war ended years ago. The novel is based on Dick's 1953 short story "The Defenders". Dick also drew upon two other of his short stories for the plot of the novel: "The Mold of Yancy" and "The Unreconstructed M".