This book is intended for advanced undergraduate and graduate students in mechanical and aerospace engineering taking a course commonly called Principles of Turbomachinery or Aerospace Propulsion. It begins with a review of basic thermodynamics and fluid mechanics principles to motivate their application to aerothermodynamics and real-life design issues. This approach is ideal for the reader who will face practical situations and design decisions in the gas turbine industry. Among the features of the book are: • An emphasis on the role of entropy in assessing machine performance • A timely review of flow structures • Revisiting the subsonic and supersonic De Laval nozzle as it applies to bladed turbomachinery components • An applied review of boundary layer principles • And highlighting the importance of invariant properties across a turbomachinery component in carrying out real computational tasks. The text is fully supported by over two hundred figures, numerous examples and homework problems.