Photochemistry is the study of the interaction of light with matter. This fascinating subject is explained in a clear yet comprehensive manner. Aimed at an undergraduate audience, the text describes the `new' chemistry that follows the absorption of light, and explains how light has this extraordinary influence on chemical behaviour. Examples of established principles are presented examining the way in which life and the other natural processes depend on photochemistry, and also how photochemistry can be used in a variety of applications.