US Dollar Index
widget... The US dollar index is computed from the exchange rate with the Euro, Yen, British Pound, Canadian Dollar, Swedish Krona and the Swiss Franc. It was introduced in 1973 and was initially set to 100. Since then, it has been as high as 160 and as low as 75.
If you're an international investor with US-denominated assets, you almost certainly want to track the US dollar. If you're an American, you should definitely be concerned with the decline of the dollar. It means more expensive imported stuff such as oil.