Which children's book features a boy named Max who sails to where the wild things are?

The children's book featuring Max sailing to where the wild things are is Maurice Sendak's Where the Wild Things Are. In the story, Max wears a wolf suit, causes trouble at home, and is sent to bed without supper.

His imagination then carries him across a body of water to an island inhabited by the Wild Things. They crown him their king, and he joins their “wild rumpus” before realizing that he wants to return home. When Max sails back, he finds his supper waiting for him, still warm. The journey is often read as a story about anger, imagination, independence, and the reassurance of returning to a loving home.

Sendak wrote and illustrated the book, which was published in 1963. Its monsters are not from a separate fairy tale or traditional legend; they are Sendak's distinctive creations. The 2009 film adaptation expanded the brief picture-book narrative, but the original book is much shorter and relies heavily on its illustrations and emotional rhythm.