The Greenspan put was a monetary policy response to financial crises that Alan Greenspan, former chair of the Federal Reserve, exercised beginning with the crash of 1987. Successful in addressing various crises, it became controversial as it led to periods of extreme speculation led by Wall Street investment banks overusing the put's repurchase agreements (or indirect quantitative easing) and creating successive asset price bubbles. The banks so overused Greenspan's tools that their compromised solvency in the 2008 financial crisis required Fed chair Ben Bernanke to use direct quantitative easing (the Bernanke put). The term Yellen put was used to refer to Fed chair Janet Yellen's policy of perpetual monetary looseness (i.e. low interest rates and continual quantitative easing).
In Q4 2019, Fed chair Jerome Powell recreated the Greenspan put by providing repurchase agreements to Wall Street investment banks as a way to boost falling asset prices; in 2020, to combat the financial effects of the COVID-19 pandemic, Powell re-introduced the Bernanke put with direct quantitative easing to boost asset prices. In November 2020, Bloomberg noted the Powell put was stronger than both the Greenspan put or the Bernanke put, while Time noted the scale of Powell's monetary intervention in 2020 and the tolerance of multiple asset bubbles as a side-effect of such intervention, "is changing the Fed forever."