Unlike many other books on chemical bonding, this introduction to the subject does not adopt the traditional historical treatment in which the two basic theories of valence, molecular orbital and valence bond, are introduced and applied to increasingly complex molecules. Instead it develops the subject area from fundamental concepts which are important in chemistry as a whole. The validity of these concepts is examined within both the older empirical models and within the more recent ab-initio calculations. In this second edition, the contents have been extended to cover the mathematical basis of ab-initio calculations and the structure of computer programs used to carry these out. The new edition has also allowed the authors to extend the coverage of group theory techniques and update aspects of transition metal chemistry.