This introductory chapter gives an overview of the key concepts discussed in the subsequent chapters of this book. The book focuses on Mega Event legacy given the increased focus and interest by both the research community and those involved in the various stages of bidding and hosting these events. It contributes to understanding legacy of mega events and acknowledges all 29 contributors for their efforts to challenge existing ways of thinking, to produce detailed and thought-provoking discussions of existing evidence and new cases/data. The use of sporting and other mega-events to bring about transformation of socially deprived areas of major cities, as well as a host of other legacy claims, are becoming an increasingly important part of the rationale behind hosting such events. Hosting mega-events has also proved both costly and difficult to budget for with, for example, the Athens Olympic Games projected budget set at US $1.6 billion and the games eventually cost nearly $16 billion.