Computational chemistry and molecular modeling is a fast emerging area which is used for the modeling and simulation of small chemical and biological systems in order to understand and predict their behavior at the molecular level. It has a wide range of applications in various disciplines of engineering sciences, such as mate- als science, chemical engineering, biomedical engineering, etc. Knowledge of c- putational chemistry is essential to understand the behavior of nanosystems; it is probably the easiest route or gateway to the fast-growing discipline of nanosciences and nanotechnology, which covers many areas of research dealing with objects that are measured in nanometers and which is expected to revolutionize the industrial sector in the coming decades. Considering the importance of this discipline, computational chemistry is being taught presently as a course at the postgraduate and research level in many univer- ties. This book is the result of the need for a comprehensive textbook on the subject, which was felt by the authors while teaching the course. It covers all the aspects of computational chemistry required for a course, with suf cient illustrations, nume- cal examples, applications, and exercises. For a computational chemist, scientist, or researcher, this book will be highly useful in understanding and mastering the art of chemical computation. Familiarization with common and commercial software in molecular modeling is also incorporated. Moreover, the application of the concepts in related elds such as biomedical engineering, computational drug designing, etc. has been added.