There is an increasing interest in the prediction of properties of materials such as substitutional alloys, their surfaces, and metallic or semiconductor multilayers. An understanding based on a microscopic, parameter-free approach is of importance for future developments in solid state physics and materials science. The purpose of this book is to provide this understanding. The text consists of two major parts. The first explores the theoretical background while the second is devoted to applications. Researchers in solid state theory, surface science and computational materials research should benefit from the book's treatment, while graduate students should find this text a suitable introduction to these topics.