This book is based on an introductory turbomachinery course at Durham University. This course was taught by Dr David Gregory-Smith and Professor Li He over a number of years and I am extremely grateful to them for providing a clear and lucid set of principles on which to base this work. My current colleagues at Durham Dr Rob Dominy and Dr David Sims-Williams have also provided invaluable help (even if they didn’t realise it!) in preparing this work.