The theory of surface electronic states is a widely researched topic which underlies all our knowledge of the behaviour of electrons at solid surfaces. It is of paramount importance in understanding the mechanics by which solid-state devices operate and catalytic reactions proceed. Nowavailable in paperback, this book provides the most current and straightforward introduction to the subject. Although the subject is viewed through the `theoretical eye' of a physicist, the topics are treated in an elementary fashion. The book is therefore accessible to all surface scientists withan understanding of quantum mechanics and some familiarity with solid state physics.