The U.S. dollar index is a measure of the value of the U.S. dollar relative to a basket of foreign currencies. The USDX was established by the U.S. Federal Reserve in 1973 after the dissolution of the Bretton Woods Agreement. It is now maintained by ICE Data Indices, a subsidiary of the Intercontinental Exchange (ICE).

The six currencies included in the USDX are often referred to as America's most significant trading partners.

The index has only been updated once, in 1999, when the newly-created euro replaced the German mark, French franc, Italian lira, Dutch guilder, and Belgian franc.