This book considerably emphasizes on the physical phenomena of gas dynamics, and the limitations of applicability of such phenomena are stressed as well. In the fourth edition, the subject matter has been given a fine tuning, clarifying the vital aspects of the flow processes associated with the compression and expansion waves. Problems with answers are included at the end of each chapter to provide the students with an opportunity to test and augment their understanding of the fundamental principles of the subject. The book is intended for the undergraduate students of mechanical and aerospace engineering.