A very comprehensive book, enabling the reader to understand the basic formalisms used in electronic structure determination and particularly the "e;Muffin Tin Orbitals"e; methods. The latest developments are presented, providing a very detailed description of the "e;Full Potential"e; schemes. This book will provide a real state of the art, since almost all of the contributions on formalism have not been, and will not be, published elsewhere. This book will become a standard reference volume. Moreover, applications in very active fields of today's research on magnetism are presented. A wide spectrum of such questions is covered by this book. For instance, the paper on interlayer exchange coupling should become a "e;classic"e;, since there has been fantastic experimental activity for 10 years and this can be considered to be the "e;final"e; theoretical answer to this question. This work has never been presented in such a complete form.