Introduction, Giovanni Caravale Part I. The idea of equilibrium in economic theorizing 1. Some considerations on the notion of equilibrium in economic theory, Giovanni Caravale Comment, Giorgio Lunghini 2. Equilibrium, Reproduction and Crisis, Giorgio Lunghini 3. Equilibrium, disequilibrium and macroeconomic theory, Alessandro Vercelli Part II. Equilibrium in the neo classical conception 4. Catholicity of General Equilibrium, Pier Carlo Nicola 5. Equality of the rates of return in models of general economic equilibrium with capital accumulation, Domenisco Tosato Comment, Pierangelo Garegnani Replay, Domenico Tosato 6. The theory of equilibrium with stochastic rationing, Gerd Weinrich Part III. Equilibrium in the Classical Conception 7. On some supposed obstacles to the tendency of market prices towards natural prices, Pierangelo Garegnan Part IV. Equilibrium in the Keynesain Conception: Economic Theory and Policy 8. The Concept of Equilibrium in the Keynesian Conception: Economic Theory and Policy 9. The concept of Equilibrium and the reality of unemployment, Bruno Jossa 9. Long-period positions and keynesian short-period equilibrium, Paola Potestio 10. On the notion of optimum disequilibrium, Luca Meldolesi