Momo, also known as The Grey Gentlemen or The Men in Grey, is a fantasy novel by Michael Ende, published in 1973. It is about the concept of time and how it is used by humans in modern societies. The full title in German translates to Momo, or the strange story of the time-thieves and the child who brought the stolen time back to the people. The book won the Deutscher Jugendliteraturpreis in 1974.

Michael Andreas Helmuth Ende was a German writer of fantasy and children's fiction. He is known for his epic fantasy The Neverending Story ; other well-known works include Momo and Jim Button and Luke the Engine Driver. His works have been translated into more than 40 languages and sold more than 35 million copies.