The Twenty-One Balloons is a novel by William Pène du Bois, published in 1947 by the Viking Press and awarded the Newbery Medal for excellence in American children's literature in 1948. The story is about a retired schoolteacher whose ill-fated balloon trip leads him to discover Krakatoa, an island full of great wealth and fantastic inventions. The events and ideas are based both on scientific fact and imagination, and the descriptions are accompanied by illustrations by du Bois.