We explore how monetary policy affects corporate investment decisions, and why there are long and variable lags in transmission. To do so, we hand-collect a firm-level dataset of U.S. investment plans and link it to managers’ cash-flow expectations. We first document new facts about investment plans. Firms' investment plans are persistent, and the initial plan explains most of the variation in realized investment. However, firms immediately update investment plans and earnings expectations in response to monetary policy shocks. We find a stronger effect on long-horizon plans than short-horizon plans. Plans for new and expansionary projects respond more to monetary policy than plans related to ongoing projects. These results help to explain the "long and variable" lags in monetary policy transmission. Regarding transmission mechanisms, we document a financing-cost channel, where policy-driven increases in borrowing costs reduce planned investment.