In his eye-popping work of picture book nonfiction, the Caldecott Honor–winning author-illustrator Steve Jenkins explains how for most animals, eyes are the most important source of information about the world in a biological sense. The simplest eyes—clusters of light-sensitive cells—appeared more than one billion years ago, and provided a big survival advantage to the first creatures that had them. Since then, animals have evolved an amazing variety of eyes, along with often surprising ways to use them.