The U.S. Dollar Index (USDX, DXY, DX) is an index (or measure) of the value of the United States dollar relative to a basket of foreign currencies, often referred to as a basket of U.S. trade partners' currencies. The Index goes up when the U.S. dollar gains "strength" (value) when compared to other currencies.
It is a weighted geometric mean of the dollar's value relative to following select currencies:
USDX started in March 1973, soon after the dismantling of the Bretton Woods system. At its start, the value of the U.S. Dollar Index was 100.000. It has since traded as high as 164.7200 in February 1985, and as low as 70.698 on March 16, 2008.
The make up of the "basket" has been altered only once, when several European currencies were subsumed by the euro at the start of 1999. Some commentators have said that the make up of the "basket" is overdue for revision as China, Mexico, South Korea and Brazil are major trading partners presently which are not part of the index whereas Sweden and Switzerland are continuing as part of the index.
|Year (last business day)||DXY Close||Factors Driving Dollar's Value|
|1967||121.79||Gold standard kept dollar at $35/oz.|
|1969||121.74||Dollar hit 123.82 on 9/30.|
|1973||102.39||Gold standard ended. Index created in March.|
|1976||104.56||Fed lowered rate.|
|1978||86.50||Fed raised rate to 20 percent to stop inflation.|
|1981||104.69||Reagan tax cut.|
|1983||131.79||Tax hike. Increased defense.|
|1985||123.55||Record of 163.83 on March 5.|
|1988||92.29||Fed raised rates.|
|1993||97.63||Balanced Budget Act.|
|1995||84.83||Fed raised rate.|
|2000||109.13||Tech bubble burst.|
|2001||117.21||Dollar rose to 118.54 on 12/24 after 9/11 attacks.|
|2002||102.26||Euro launched as a hard currency at $.90.|
|2003||87.38||Iraq War. JGTRRA.|
|2005||90.96||War on Terror doubled debt. It weakened the dollar.|
|2007||76.70||Euro rose to $1.47.|
|2008||82.15||Record low of 71.30 on 3/17.|
|2009||77.92||ECB lowered rates.|
|2011||80.21||Operation Twist. Debt crisis.|
|2012 - 2013||79.77||QE3 and QE4. Fiscal cliff.|
|2013||80.04||Taper tantrum. Government shutdown. Debt crisis.|
|2014||90.28||Ukraine crisis. Greek debt crisis.|
|2015||98.69||Fed raised rates.|
ICE provides live feeds for Dow Futures that appear on Bloomberg.com, Money.CNN.com, DollarIndex.org. USDX is updated whenever U.S. Dollar markets are open, which is from Sunday evening New York City local time (early Monday morning Asia time) for 24 hours a day to late Friday afternoon New York City local time.
The U.S. Dollar Index is calculated with this formula: USDX = 50.14348112 × EURUSD-0.576 × USDJPY0.136 × GBPUSD-0.119 × USDCAD0.091 × USDSEK0.042 × USDCHF0.036 
The U.S. Dollar Index, together with all rights, title and interest in and related to the U.S. Dollar Index, including all content included therein (including, without limitation, it's formulation, components, values, weightings and methods of calculation), and all related intellectual property and property rights, is the exclusive property of ICE Futures U.S., Inc.