The sharp deterioration of the public finances in many countries has revived interest in a "capital levy" -- a one off tax on private wealth -- as an exceptional measure to restore debt sustainability. The appeal is that such a tax, if it is implemented before avoidance is possible and there is a belief that it will never be repeated, does not distort behavior (and may be seen by some as fair). There have been illustrious supporters, including Pigou, Ricardo, Schumpeter, and, until he changed his mind - Keynes. The conditions for success are strong, but also need to be...