This paper investigates the impact of tax changes on economic activity. We use the narrative record, such as presidential speeches and Congressional reports, to identify the size, timing, and principal motivation for all major postwar tax policy actions. This analysis allows us to separate legislated changes into those taken for reasons related to prospective economic conditions and those taken for more exogenous reasons. The behavior of output following these more exogenous changes indicates that tax increases are highly contractionary. The effects are strongly significant, highly robust, and much larger than those obtained using broader measures of tax changes. (JEL E32, E62, H20, N12) Tax changes have been a major public policy issue in recent years. The tax cuts of 2001 and 2003 were passed amid firestorms of debate about their likely effects. Some policymakers claimed that the cuts would both stimulate the economy in the short run and increase normal output in the long run. Others argued that they would raise interest rates and lower confidence and thereby reduce output in both the short run and the long run. That views of the effects of tax changes vary so radically largely reflects the fact that measuring