Empirical models have failed to explain inflation behavior over the last 20 years in most developed economies. The unusual inflation dynamics—the ‘missing deflation’ during recessions and the ‘missing inflation’ during recoveries—points to a failure of Phillips curve predictions. Several hypotheses have been proposed to explain the ‘twin puzzle’ phenomenon while at the same time have imposed challenging implications to conduct monetary policy. It is of utmost importance to understand the challenges for monetary policy conduct in an environment where inflation dynamics is hard to unravel. This volume contributes to the study of the ‘twin puzzle’ phenomenon and the challenges facing monetary policy. It gathers a selective group of distinguished scholars and policy makers to discuss the latest academic findings on inflation dynamics.