Major sovereign bond markets are the cornerstone of the financial system. They not only provide a method for governments to raise funds but also offer low-risk, long-term assets for pension funds and insurance companies to invest in, serve as a yardstick for other asset prices, and give investors a means to hedge interest rate risks. Yet, their smooth functioning cannot be taken for granted. Flashes of extreme volatility have punctuated periods of extraordinary calm. This year, record amounts of European and Japanese government bonds—as much as $6 trillion—yielded negative interest, implying that lenders paid governments to borrow rather than the other way around. What does this mean for markets, investors, and the global economy?