For the last quarter of a century, we have been living in a financial world,which succeeded the industrial world and an earlier agricultural world. The world's major companies do not make use of their real power except to bring together the funds needed to conclude financial operations that are sure to produce vast profits. Even national governments are powerless to regulate their currencies as they wish and they must often bow down to the dictates of international finance. What brought about this structural upheaval? In his book, Nicolas Bouleau, who is a professor at the Ecole des Ponts-et-Chaussées, shows how the application of mathematics to finance has turned the latter into an exact science, as well as a formidable and efficienct tool. This is not a textbook on financial mathematics, but an essay on the new economic situation.