The dollar has plunged to its lowest level against the euro since April 2005 amid concerns for the US economy.
The euro surged to $1.3086 against the dollar, with many other currencies following suit.
Sterling rose almost 1% to $1.93, the yen hit a two-month high and Russia's rouble rose to a seven-year high.
Analysts have voiced concerns about the US economy after the White House downgraded its growth forecasts amid a sharp slowdown in the housing market.
The low dollar we have had the last few years has actually helped the US, as exports have gone up sharply. But we are still highly dependent on imports of basic goods, and if the dollar gets near $1.5 euro it is going to be a big problem.
As for why it is moving again, the European market is showing strength and the US market is showing weakness. The switch in Congress was probably the shock that set off the slide, but that sort of thing doesn't control the market.
Jay