I assess the real effects of monetary policy shocks by estimating a vector autoregressive framework with a rich lag structure on a long postwar U.S. sample. I find robust evidence of a “two-wave” effect: monetary policy shocks trigger a short-run cycle, followed by a longer-run one. I associate the second cycle with a productivity channel: monetary policy shocks generate long-run reactions in R&D spending and TFP, but not through increased innovation at the technological frontier. Crucially, evidence of the two-wave effect is driven by monetary policy easings, while policy tightenings generate standard short-run real activity responses. My results are robust to alternative econometric specifications and identification strategies. These findings have important implications for both macroeconomic modeling and the design of monetary policy.