Daron Acemoglu is the Elizabeth and James Killian Professor of Economics at the Massachusetts Institute of Technology and the recipient of the John Bates Clark Medal in 2005. He is the author of numerous works including Economic Origins of Dictatorship and Democracy, with James Robinson (Cambridge University Press, 2006) and Introduction to Modern Economic Growth (2009). He is the current editor of Econometrica. Manuel Arellano is a Professor of Econometrics at CEMFI, Madrid. His many published articles have appeared in numerous journals, including Econometrica, the Journal of Econometrics, and The Economic Journal. He is the author of Panel Data Econometrics (2003) and currently serves as second vice-president of the Econometric Society. Eddie Dekel is the William R. Kenan, Jr, Professor of Economics at Northwestern University and Grace and Daniel Ross Professor of Economics at Tel-Aviv University. He is a member of the American Academy of Arts and Sciences, a past editor of Econometrica and a current associate editor of Theoretical Economics and the Journal of Economic Literature.