How does the US's QE programme work?

Global markets have been shaken in recent weeks by concerns that the US Federal Reserve may begin scaling back its stimulus programme.

The Fed is pumping $85bn (£54bn) a month into the economy, in a programme of quantitative easing (QE).

But what is QE exactly?

Sharanjit Leyl asked Nobel Prize winning economist Thomas Sargent about the mechanics of QE and what the impact may be.