The Monster at the End of This Book is a Sesame Street book starring Grover. Upon seeing the title of the book, Grover encourages you to stop turning pages, lest we run across the scary monster foretold. As you continue turning pages, he becomes increasingly distressed, and makes every attempt to stop you, the reader.
Like many classic Sesame Street stories, this one is humourous and enjoyable, and has a surprise ending. As such, this was one of my favourite Sesame Street books growing up, probably second to Oscar's Book.
They more recently made a sequel titled Another Monster at the End of This Book with Elmo encouraging you to turn the pages while Grover played his traditional role. The sacrilege of it all!