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 performanceA timely review of flow structuresRevisiting the subsonic and supersonic De Laval nozzle as it applies to bladed turbomachinery componentsAn applied review of boundary layer principlesAnd 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.