Some knowledge of the principles of quantum mechanics and how they are applied to theoretical chemistry, it is generally agreed, should be part of the education of all chemists. This instruction in quantum chemistry is either added to the more traditional topics of physical chemistry or given separately; at Syracuse University it forms the third semester of the physical chemistry sequence. While a wide variety of textbooks and monographs on the subject of quantum chemistry exists, the author of the present text found that none of them was satisfactory for his purposes, i. e. , none fit his ideas of what subjects should be discussed and in what way. This book is presented with the hope that others with similar experiences will agree with him and endorse his conclusions. The undergraduate student to whom our attentions are directed is a chemistry major, but probably will not go on to graduate school in physical chemistry. He may take several more chemistry courses as an undergraduate and then seek a position in industry, or perhaps he will do graduate work in organic or inorganic chemistry. (Of course, one never stops hoping that, as a result of this first course, he will decide to learn more quantum chem­ istry.