This is the third edition of the successfultext-reference book that covers computational chemistry. It features changes tothe presentation of key concepts and includes revised and new material withseveral expanded exercises at various levels such as 'harder questions' forthose ready to be tested in greater depth -this aspect is absent from other textbooks in the field. Although introductoryand assuming no prior knowledge of computational chemistry, it covers theessential aspects of the subject. There are several introductory textbooks oncomputational chemistry; this one is (as in its previous editions) aunique textbook in the field with copious exercises(and questions) and solutions with discussions. Noteworthy is the fact that itis the only book at the introductory level that shows in detail yet clearly howmatrices are used in one important aspect of computational chemistry. Italso serves as an essential guide forresearchers, and as a reference book.