Using large, plausibly exogenous shocks to the maturity structure of U.S. government debt, I find that a higher supply of long-term government bonds increases firms’ discount rates at long horizons leading to a crowding-out of long-duration investment. This crowding out occurs through reallocations of capital away from long-duration investment towards short-duration investment. This happens across industries, within industries across firms and within firms across divisions. Such changes to the average duration of investment explain a significant share of changes to the average maturity of corporate debt. These results identify important real effects of policies which affect the net supply of long-termbonds, such as quantitative easing by central banks.