The decision of the Danmarks Nationalbank to lower its policy rate below zero in July 2012 was an important extension of monetary policy. We have had non-standard monetary policies, such as quantitative easing and forward guidance, since the Global Crisis of 2008, but negative nominal interest rates in Denmark represented an unprecedented leap across the mythical zero lower bound (ZLB). Of course, the ZLB has subsequently proven to be quite porous, as Switzerland, Sweden, the euro area, and Japan have also enacted negative rates.