The agile model of software development took the world by storm in 2001. By 2002, there were books and conferences on agile development. By 2006, it has influenced everything from procurement contracts to military procurement procedures, to college curriculum to project management. Six years ago Alistair Cockburn wrote the first edition of this book right after the crafting of the Manifesto for Agile Software Development. Since then a LOT has changed and with it a need for a revised edition that reflects the current picture of agile development. The first edition asked "What does this mean?" This revised edition goes beyond the basic question and now answers: "Where does agile fit in the total set of development situations?"; "How do we blend these ideas with others?"; and eventually "How do we extend these ideas to other fields?" In addition the cooperative game model grew alongside the agile model, striking a chord with business people as well as developers, making this a timely and essential revision for agile development.