Cross-country differences in austerity, defined as government purchases below forecast, account for 75 percent of the observed cross-sectional variation in GDP in advanced economies during 2010-2014. Statistically, austerity is associated with lower GDP, lower inflation and higher net exports. A multi-country DSGE model calibrated to 29 advanced economies generates effects of austerity consistent with the data. Counterfactuals suggest that eliminating austerity would have substantially reduced output losses in Eu- rope. Austerity was so contractionary that debt-to-GDP ratios in some countries increased as a result of endogenous reductions in GDP and tax revenue.