The objective of this textbook is to develop the basics of computational chemistry and molecular simulation methods in a manner that is understandable by senior undergraduate students and by beginning graduate students in engineering and the physical and life sciences. From Bohr's studies of the atom to quantum wave mechanics, the book presents the significant historical events. Chapters also discuss the functional methods related to these developments. Fundamental principles are presented in sufficient detail for the reader to appreciate the limitations and advantages of each approach. In additional, each chapter offers a number of example problems to illustrate the applicability of computational chemistry. Each chapter also offers a number of example problems to illustrate the relevance and applicability to computational chemistry. In addition, the same treatment is given to the field of molecular dynamics and mechanics. Specific examples show the application of the fundamental principles of computational chemistry and molecular simulation to materials science, engineering, and life sciences. Detailed problem sets are given at the end of each chapter which can be solved by using a variety of commercial and freeware software packages.