Assets held by money market funds, private equity firms and other entities that make up the so-called shadow banking system stood at $67 trillion worldwide at the end of last year, according to new report by the Financial Stability Board. Supporters credit shadow banks with providing valuable services; critics warn that their lack of oversight poses systemic risk. One certainty is that they're big, with half as many assets as conventional banks, by FSB's count. Here's a look at how it defines shadow banks.

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