The consequences for the proper conduct of monetary policy of the existence of a lower bound of zero for overnight nominal interest rates has recently become a topic of lively interest. In Japan the call rate (the overnight cash rate analogous to the federal funds rate in the United States) has been within 50 basis points of zero since October 1995, and it has been essentially equal to zero for most of the past four years (figure 1). Thus the Bank of Japan has had little room to further reduce shortterm nominal interest rates in all that time. Meanwhile Japan’s growth has remained anemic, and prices have continued to fall, suggesting a need for monetary stimulus. Yet the usual remedy—lower short-term nominal interest rates—is plainly unavailable. Vigorous expansion of the monetary base has also seemed to do little to stimulate demand under these circumstances: as figure 1 also shows, the monetary base is now more than twice as large, relative to GDP, as it was in the early 1990s.