A very comprehensive book, enabling the reader to understand the basic formalisms used in electronic structure determination and particularly the "Muffin Tin Orbitals" methods. The latest developments are presented, providing a very detailed description of the "Full Potential" 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 todays 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 "classic", since there has been fantastic experimental activity for 10 years and this can be considered to be the "final" theoretical answer to this question. This work has never been presented in such a complete form.