Michal Kalecki’s (1899-1970) mathematical business-cycle model first appeared as ‘Proba teorii koniunktury’ in 1933.6 This Polish essay was read in French as ‘Essai d’une théorie des mouvements cycliques construite à l’aide de la mathématique supérieure’ at the Econometric Society in Leiden in 1933. Its essential part was translated into English as ‘Macrodynamic theory of business cycles’, and was published in Econometrica in 1935. A less mathematical French version was published in Revue d’Economique Politique, also in 1935. The English paper was discussed in Tinbergen’s survey of quantitative business-cycle theories (1935b), appearing in the same issue of Econometrica. The model ingredients are summarised in Figure 1.1.