Imagine a bank that pays negative interest. Depositors are actually charged to keep their money in an account. Crazy as it sounds, several of Europe’s central banks have cut key interest rates below zero and kept them there for more than a year. Now Japan is trying it, too. For some, it’s a bid to reinvigorate an economy with other options exhausted. Others want to push foreigners to move their money somewhere else. Either way, it’s an unorthodox choice that has distorted financial markets and triggered warnings that the strategy could backfire. If negative interest rates work, however, they may mark the start of a new era for the world’s central banks.

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