The main object of this book is to present the subject of "Internal Combustion Engines" for a bachelor’s degree in mechanical engineering helpful to postgraduate students and platform article covers the syllabi of majority of the University. This book will also be highly useful intended serve as a reference book for engineers working in the field of manufacturing and maintenance of engines as well as for workers in the field of teaching. The book is written in simple and lucid language with good diagrammatic illustrations. The various topics are explained right from the fundamentals so as to build an understanding of conceptual and emphasize the relationship between conceptual and problem solving for both types of engines (spark – ignition (SI) and compression – ignition (CI) engines operating on four – stroke and two – stroke cycles). My goal has been to help the students acquire a solid theoretical background of Internal Combustion Engines; solved numerical examples are used extensively throughout the text to help them understand how theory is applied to analyze practical application.