While the world has stepped into the century of cities, the emergence of the megacity is perhaps the most visible expression of the mega-trend urbanization. This introductory chapter discusses some features that characterize the megacity beyond its extraordinary population size. Furthermore, it outlines the main objectives of this book, discusses the key concepts risk, sustainability and governance and further elaborates on why and to what extent megacities are places of opportunities and risks. The chapter describes the geographical focus – Latin America – with Santiago de Chile as an anchor city and closes with a brief overview of the book.