Has the decline in real (inflation-adjusted) interest rates over the last 30 years been driven by variations in desired saving and investment, as commonly presumed? And is this a useful way of thinking about the determination of real interest rates more generally, at least over long horizons? This column finds that this is not the case by systematically examining the relationship between several saving-investment drivers and market real interest rates (as well as estimates of natural rates) since the 1870s and for 19 countries. By contrast, a clear and robust role for monetary policy regimes emerges. The analysis has significant implications for the notion of monetary neutrality and policymaking.