This book primarily intended to serve as a textbook for B.Sc. general and Honours students. The Students of Chemistry at the post-graduate are heavily tortured by the description and theoretical approach, which make it difficult for them to grasp the subject particularly quantum chemistry. the present book is the result of such efforts in this direction. This book contains 12 chapters. All the chapters have described in step by step method with easy to understand language. At the same time, the students pursuing post-graduate courses in Quantum Chemistry and other professional courses will also find the book examples and illustrated further with the solved problems. At the end of each chapter practice problems have been added for the benefit of the readers.