This is a new book and not simply a collection of essays. Although based on some essays, it differs from them in various ways. I have changed all of them to some degree, and I have extensively rewritten many of them so as to present the material as effectively as possible and to reflect the limited number of ways in which my views have changed since the essays were written. Moreover, I have devised titles of parts, sections, and chapters that are intended to guide the reader through the complexities of the subject matter, and I have organized the material in a way that displays clearly the phases and sequence of Léon Walras's modeling of markets. In most cases, the chapters have titles that differ from those of the essays. I have eliminated most of the repetitions that are to be found in the essays, but I found that preserving some of the repetitions is desirable.

In a general way, the book accomplishes three major tasks. First, by emphasizing the concept of models in relation to Walras's work, it becomes possible to identify many of his constructions that have until now been passed over as comments on the real economy or as brief speculations about economic relationships, or that have escaped notice altogether. The word “model” rather than “theory” will ordinarily be used in reference to Walras's work because in many instances he defined special situations not found in reality and created a variety of different hypothetical constructions relating to the same general subject matter.