We haven’t yet faced the sticky widespread problem of negative interest rates among conventional U.S. Treasury bonds that has beleaguered wide swaths of the global bond market (although some Treasury Inflation-Protected Securities have posted negative yields). There’s currently a heated debate about the long-term impact of negative rates on global economic growth, the financial sector, and investor behavior, and some of the early evidence isn’t comforting.

But while the financial press has widely reported on the growing inventory of bonds across the globe trading at negative yields, few have explained clearly how negative rates actually work or why they’ve come about.