This new book has been written to provide a simple explanation of how a steam locomotive works and is designed to appeal to the widest possible audience, using clear explanations and diagrams, generous in number yet straightforward in context. Steam railway volunteers and enthusiasts come from all walks of life and often do not have an engineering background. Therefore, the process of learning the required knowledge to work with steam locomotives, or simply to develop a further understanding, can take considerable time because the best current texts on the subject were originally written to aid staff working through apprenticeships during the steam era. To address the needs of today's readers, the complex engineering of the steam locomotive is unraveled by use of a large number of easily understandable diagrams, explaining the function of the components in a step-by-step manner. There is no technical knowledge required on the part of the reader, nor is there any requirement to understand engineering drawings, because the diagrams and explanations are carefully approached. Nevertheless, the book should also appeal to the technically minded, as there are few who understand the steam locomotive in its entirety, a subject which encompasses many engineering specialisms including structures, dynamics, thermo-dynamics and fluid flows. Starting with a basic introduction to the principle of the steam locomotive boiler, the book goes on to provide explanations of both coal and oil firing. Further detailed chapters cover all the essential components, including gauge glasses, injectors, control valves, mainframes, cylinders, valve gears, lubrication, air brakes, vacuum brakes, auxiliaries and cab layouts.