Many candidate explanations for the low level of real interest rates have been put forward. Less progress has been made on bringing together the different hypotheses into a unifying framework, on quantifying their relative importance and on predicting the future path for real interest rates. This column attempts to fill that gap, and suggests that persistent shifts to global desired savings and investment are behind the bulk of the fall in real interest rates. Those trends are unlikely to unwind anytime soon, so that the global equilibrium rate is likely to remain low, perhaps settling at or below 1% in the medium to long-run.