David A. Adler is a former math teacher and author of more than two hundred books for children.  He has collaborated on several science picture books with Anna Raff, including Things That Float and Things That Don't and Light Waves, a finalist for the SB&F Prize for Excellence in Science Books.  He is also the author of the Picture Book Biography series, the Cam Jansen mystery series, as well as books on math and history. He lives in New York. Anna Raff is an award-winning illustrator of children's books. She illustrated David A. Adler's Simple Machines and Things That Float and Things That Don't, which received starred reviews from both Booklist and Publishers Weekly. She lives in New York City.