This book is confined to a presentation of the thermodynamic and aerodynamic theory forming the basis of gas turbine design, avoiding as far as possible the many conlroversial topics associated with this new form of prime-mover. While it is perhaps too early in the development of the gas turbine to say with complete assurance what are the basic principles involved, it is thought that some attempt must now be made if only to fill the gap between the necessarily scanty outline of a lecture course and the many articles which appear in the technical journals. Such articles are usually written by specialists for specialists and presuppose a general knowledge of the subject. Since this book is primarily intended for students, for the sake of clarity some parts of the work have been given a simpler treatment than the latest refinements of method would permit. Care has been taken to ensure that no fundamental principle has been misrepresented by this approach.