How did we come to this? Everything seemed to be going well, the world's economic growth was the fastest ever in history; everything led us to believe that this was going to continue, all around the world, thanks to abundant savings and outstanding technical progress. Then, without any warning, we found ourselves at the dawn of the most serious global recession for eighty years. On the face of it, nothing seemed to happen between these two events, except that some American families found themselves unable to continue to repay their mortgages. The goal of this book is to explain this mystery as simply as possible, with a view to solving it, in order to prevent the crisis from deteriorating into a worldwide political catastrophe and to insure that it never happens again.