Kenneth J. Arrow’s contributions to knowledge in the twentieth century can only be compared with the contributions of giants such as Kurt Godel,Alan Turing or John von Neumann. It is on purpose that I write knowledge rather than economics because these contributions go well beyond economics to encompass political science, mathematics, operations research, and philosophy. I will restrict myself here to economics, only mentioning in passing the other domains. Regarding economics, the main contributions are his works on social choice theory, general economic equilibrium, individual choice theory, the treatment of uncertainty in general equilibrium models, and information theory. In particular, Arrow’s name is associated with two topics of paradigmatic importance for modern economics: the Arrow (im)possibility theorem and Arrow-Debreu equilibrium (along with Gerard Debreu)