Carlos Álvarez-Nogal is Professor of Economic History at Universidad Carlos III de Madrid and Visiting Professor at Stanford University, Caltech and Paris School of Economics. Christophe Chamley is Professor of Economics at Boston University, Emeritus Professor EHESS at the Paris School of Economics, holder of a Cátedra de Excelencia in 2014 at Universidad Carlos III de Madrid, fellow of the Econometric Society and author of Rational Herds: Economic Models of Social Learning (2004).