This persuasive book makes the novel argument that highly developed countries should eventually eliminate paper money altogether, at least for large transactions, and that they should eliminate high-denomination notes—for example, the $100 bill and the 500 euro bill—as soon as practically possible. Such notes are rarely used in ordinary transactions and often support criminal activities and tax evasion. The book also addresses some of the cash-related problems that today’s low-interest environment poses to monetary policy. Paper currency—which, in effect, is the equivalent of interest-free government debt—limits the extent to which interest rates can become negative, which might be desirable under some conditions, including those that have prevailed in recent years. Although phasing out paper currency would introduce some inconveniences, Rogoff argues that the benefits would far outweigh the costs. It’s an important and thought-provoking proposal.