Thus Spoke Zarathustra: A Book for All and None (German: Also sprach Zarathustra: Ein Buch für Alle und Keinen) is a philosophical novel by German philosopher Friedrich Nietzsche, composed in four parts between 1883 and 1885. Much of the work deals with ideas such as the "eternal recurrence of the same", the parable on the "death of God", and the "prophecy" of the Übermensch, which were first introduced in The Gay Science.

Described by Nietzsche himself as "the deepest ever written," the book is a dense and esoteric treatise on philosophy and morality, featuring as protagonist a fictionalized prophet descending from his mountain retreat to mankind, Zarathustra. A central irony of the text is that Nietzsche mimics the style of the Bible in order to present ideas which fundamentally oppose Christian and Jewish morality and tradition.