The Zero Lower Bound (ZLB) or Zero Nominal Lower Bound (ZNLB) is a macroeconomic problem that occurs when the short-term nominal interest rate is at or near zero, causing a liquidity trap and limiting the central bank's capacity to stimulate economic growth. The problem of the ZLB returned to prominence with Japan's experience during the 90's, and more recently with the subprime crisis. The belief that monetary policy under the ZLB was effective in promoting economy growth has been critiqued by Paul Krugman, , and Michael Woodford among others.