Interaction of light and matter produces the appearance of materials. To deal with the immense complexity of nature, light and matter is modelled at a macroscopic level in computer graphics. This work is the first to provide the link between the microscopic physical theories of light and matter and the macroscopic process of rendering realistic images. This enables prediction of appearance based on the contents and the physical conditions of a material. The idea is to take the contents declaration for a material and use it to predict what the material looks like. Or conversely, to take a picture of a material and determine the contents of the material. The book is in four parts. Part I provides the link between microscopic and macroscopic theories of light. Part II describes how to use the properties of microscopic particles to compute the macroscopic properties of materials. Part III illustrates that we can use geometrical models to handle the large number of variables which appear when we construct appearance models from microscopic theories. Finally, Part IV provides detailed appearance models for natural water, ice, and milk to demonstrate how the theory is applied.