We want to make GDP the measure of everything - performance, well-being, quality of life - when it only represents a measure of market economic activity. On the contrary, it is possible to construct reliable measures of the material determinants of well-being, income distribution, quality of life, the sustainability of current developments and many other aspects of our economy and society. This is even essential if we want society to recognize itself more in the image that the mirror of statistical data reflects back to it and, above all, if we want to make informed decisions about the future. To face the future, we must first better decipher the world around us and better perceive how it is changing. There is no other way out than to improve the Arithmetic of Nations. This is precisely what this book proposes. Joseph Stiglitz is the 2001 Nobel Prize winner in Economics. After serving as Chief Economist and Senior Vice President of the World Bank, he is a professor at Columbia University in New York. Amartya Sen is the 1998 Nobel Prize winner in Economics. He is a professor at Harvard University. Jean-Paul Fitoussi is a professor at the Institut d'études politiques de Paris. He is also President of the French Economic Observatory.