This is a book about things in magnetism that interest me. I think that these are important things which will interest a number of other chemists. The restriction is important, because it is difficult to write well about those things which are less familiar to an author. In general, the chemistry and physics of coordination compounds are what this book is about. Magnetochemistry is the study of the ground states of metal ions. When the ions are not interacting, then the study of single-ion phenomena is called paramagnetism. When the metal ions interact, then we are concerned with collective phenomena such as occur in long-range ordering. Several years ago, Hans van Duyneveldt and I published a book that explored these subjects in detail. Since that time, the field has grown tremendously, and there has been a need to bring the book up to date. Furthermore, I have felt that it would be useful to include more subsidiary material to make the work more useful as a textbook. This book is the result of those feelings of mine.