This book is about an idea. The idea is conceptualised in two simple words, ‘sporting capital’. But contained in these two words are multiple layers of meaning that span subject matter as diverse as individual human behaviour, motivational psychology, physical motor development, pedagogy, political sciences, philosophy, cultural studies and social policy. Sporting capital is not an abstract idea, but is an idea with a purpose in the sense that it is ‘a thought or suggestion as to a possible course of action’. In writing this book I have taken the germ of this idea to build a coherent theory defined as ‘a set of principles on which the practice of an activity is based’. Theories evolve and are there to be tested and challenged in the real world. The theory of sporting capital provides a framework for empirical research and a guide to policy and action. It is a theory that is very much in its infancy insofar as it has yet to undergo thorough ‘road testing’; but all theories have to start somewhere, and those putting them forward must, with an open mind, be prepared to take some bumps and bruises along the way. As we go down that road I anticipate healthy and constructive criticism but am optimistic that sporting capital will emerge as a theory whose time has come.