His research focuses on the accumulation and distribution of global wealth, from both a public finance and international macro perspective. He is particularly interested in the role of tax havens in the global economy. Recent work includes "The Missing Wealth of Nations: Are Europe and the U.S. net Debtors or net Creditors?|" (Quarterly Journal of Economics, 2013), and ", 2013), and "Capital is Back: Wealth-Income Ratios in Rich Countries, 1700-2010|" (with Thomas Piketty).