How severe has the zero lower bound constraint been?: Summary In December 2008, the Fed lowered the federal funds rate to essentially zero and has kept it there since then. This column argues that, contrary to traditional macroeconomic thinking, monetary policy has not been severely constrained by the zero bound until mid-2011. The results imply that the Fed could have done more to ease monetary policy between 2009 and 2011. These findings could also help explain why the fiscal stimulus package adopted in 2009 did not bring the expected success.