This is an excerpt from the 4-volume dictionary of economics, a reference book which aims to define the subject of economics today. 1300 subject entries in the complete work cover the broad themes of economic theory. This extract concentrates on the topic of general equilibrium, a central theme in modern economic theory - the economy considered as a system of interrelated markets. The essays in this volume trace the evolution of general equilibrium theory from Wald and Walrus through Arrow, Debreu and McKenzie to the present day. The collection illuminates one of the grand theemes of 20th century economic thought.