This paper describes developments in real long-term interest rates in the main OECD economies and surveys their various determinants. Real long-term government bond yields declined from the 1980s to very low levels in the recent period, though they have not reached the historical lows of the 1970s. The decline in real interest rates has been driven by a combination of factors whose importance has varied over time. In the 1990s, the decline in inflation levels and in volatility was key. In the 2000s, purchases of US government bonds by official investors in emerging market economies, played an important role. More recently, quantitative easing and other unconventional monetary policy action, and possibly the Basel-III-induced increase in bank demand for safe assets, have been main drivers. Higher perceptions of risks after the last crisis do not seem to have put lasting downward pressures on government bond yields.