Quantum chemical calculation method has become an indispensable tool in exploring chemistry. However, for the inborn difficulty of quantum chemistry the beginners hesitate to adopt this powerful tool in their research. This book provides various specific examples and exercises. They are appropriately chosen to improve your capability. When I have some problems in determining which basis set must be selected and the theoretical level at which calculation will be processed, this book is a good guide to me. Although all the content is based on only one commercial packge(Gaussian series), I would like to recommend this book to all scientists who have interests in computational chemistry.