Thus Spoke Zarathustra is a work of philosophical fiction written by German philosopher Friedrich Nietzsche between 1883 and 1885. The protagonist is nominally the historical Zarathustra but besides a handful of sentences Nietzsche is not particularly concerned with any resemblance. Much of the book purports to be what Zarathustra said and it repeats the refrain "Thus spoke Zarathustra".

The style of Zarathustra has facilitated variegated and often incompatible ideas about what Zarathustra says. Zarathustra's "[e]xplanations and claims are almost always analogical and figurative". Though there is no consensus with what Zarathustra means when he speaks there is some consensus with what he speaks about. Zarathustra deals with ideas about the Übermensch the death of God the will to power and eternal recurrence.

Zarathustra himself first appeared in Nietzsche's earlier book The Gay Science. Nietzsche has suggested that his Zarathustra is a tragedy and a parody and a polemic and the culmination of the German language. It was his favourite of his own books. He was aware however that readers might not understand it. Possibly this is why he subtitled it A Book for All and None. But as with the content whole the subtitle has baffled many critics and there is no consensus.