A remarkable exploration of how shadows have forever fascinated us: their extraordinary hold on our fears and imagination; their importance to astronomers, scientists, philosophers, and artists; their influence on myth and religious beliefs. What's stranger than a shadow? Shadows are messengers from the world of darkness, images that we can't shake off, black spots that have troubled our sleep through the ages. And yet shadows have been the key to unlocking some of our toughest scientific problems: the reason for eclipses, the distances between planets, the shape and size of the earth, the structure of the solar system, the nature of time itself. In this unique study-combining history, science, and anthropology-Roberto Casati discusses the famous and the obscure who, armed with imagination and creativity, struggled with the concept of shadow and provided us with explanations of and uses for our constant companion. Among those who were part of this shadow club were Eratosthenes and Galileo, ancient Arab astronomers and modern mathematicians, classical Greek painters and Leonardo da Vinci.