The 1930s coincided with a radical change in the way macroeconomic issues were addressed. From then on, macroeconomics became a quantitative sub discipline based on mathematical models. This book describes and analyzes that evolution by paying attention to a series of models developed by economists who became the most recognized names of the profession, as well as by other economists much less known today. In explaining how they were created and how they embodied specific visions of the world, we hope to help an informed public to reflect upon the past and the ideals of
a generation of economists that came of age during the interwar and early postwar period. In addition, our ambition is to provide new materials to economists, students, teachers and social scientists eager to gain a new perspective on the kind of knowledge which belongs, for a significant part, to the modern landscape of economics.

One of the central themes of this book, which appears throughout the models studied, is the problem of economic instability, whose treatment varied according to the models and the events surrounding them. Part of the challenge of writing this history was to find a way to account for the technical dimension of these contributions without diluting their originality in simplifications. The book has thus been written in relation to a website providing computer simulations which offer a way to easily visualize the solutions of different models and to see how policies may change economic trajectories. In order to stick with the message and the vision of the original contributors, these applications have been developed in strict accordance with the properties of the models studied. Furthermore, this website has been designed to provide an easier access to the content of the archival and published materials forming the basis of this study, as well as a sort of mathematical appendix to the book. It is our conviction that such a tool may contribute to the consolidation of our knowledge of the past and help complete the big picture of the development of economic ideas.

We are also confident that this approach can meet the expectations of economists who, for teaching purposes, often refer to past discussions but who, in the absence of a precise historical account, often resort to schematic views which poorly fulfill the objectives pursued. One just has to look at the introduction of classic papers and textbooks to measure the gap between their content and what is usually said about them. In providing a new way to look at the past,we thus hope to avoid two obstacles: falling back on scholarly works understood by a handful of experts on one hand, or on the other hand, falling back on the “potted” histories full of approximations and simplifications.