As stated on its frontispiece, the aim of this book is "to familiarize researchers and graduate students in both physics and mathematics with the application of non-associative algebras in physics." And it does precisely that. This is a clear, brief, and authoritative introduction to the ongoing search for natural applications of octonions to physics, an effort being made by a small number of enthusiastic devotees. Apart from this book, I know of no other introduction to the subject. As such, the book fills a gap in the literature of physics. Professor Okubo is a well-known mathematical physicist, and the book has a clear-headed, right-to-the-point, no-digression style that is reminiscent of Dirac's books, particularly his book on general relativity.