May 13, 1997 The short-run Phillips curve describes a positive short-run relationship between the level of economic activity and inflation. When the level of demand in the economy as a whole runs ahead of the level of output that the economy can supply in the short run, price pressures increase and inflation rises. This article reviews the origins of the short-run Phillips curve with particular emphasis on the long-standing idea that the shape of this curve may be non-linear, with inflation becoming more sensitive to changes in output when the cycle of economic activity is high than when it is low. This type of non-linearity in the short-run Phillips curve, which is typically motivated by the effects of capacity constraints that limit the ability of the economy to expand in the short run, has recently attracted renewed attention. The article surveys recent research that finds some evidence of this type of non-linearity in the Phillips curve in Canada and considers the potential implications for monetary policy.