The U.S. Dollar Index tracks the strength of the dollar against a basket of major currencies. DXY was originally developed by the U.S. Federal Reserve in 1973 to provide an external bilateral trade-weighted average value of the U.S. dollar against global currencies. U.S. Dollar Index goes up when the U.S. dollar gains "strength" (value), compared to other currencies. The following six currencies are used to calculate the index:
U.S. Dollar Index is just a number that lets you track performance of the instruments comprising the index, so you can't invest in it directly. But you can buy U.S. Dollar Index futures or funds or invest in its components.
The lowest ever quote of U.S. Dollar Index is 70.70 USD. It was reached on Mar 17, 2008.
U.S. Dollar Index reached its highest quote on Feb 25, 1985 — 164.72 USD.