The currency pair USD/CHF is the rate between the US dollar and the Swiss franc. As in all currency pairs where the euro is not involved, the US dollar is the base currency in exchanges with the Swiss franc, and the franc is the quote or counter currency.
In times of economic difficulty in the USA, the USD/CHF pair traditionally sees a lot of action in forex trading. The Swiss Franc is renowned as a safe haven currency because Switzerland has a tradition of extremely low inflation. Until 2000, it also had a legal requirement that the franc must be backed by a minimum of 40% gold reserves, although this was formally ended by referendum, gold remains 20% of all Swiss assets.
The history of the USD/CHF pair goes back to the end of the Second World War when Switzerland pegged the franc to the US dollar at $1 = 4.30521 francs, this was changed four years later to the altogether tidier $1 = 4.375 francs.
In the first decade of this millennium the Swiss franc maintained a steady exchange rate with the euro at 1.55CHF per euro. This meant that the franc gradually made gains against the dollar as the euro strengthened, eventually leading to value parity between the franc and the dollar for the first time in March 2008.
Since then, following troubles in the eurozone and the US, the franc has continued to gain ground. In March 2011 it passed $1 = 0.91CHF (one franc equalling $1.10) and in June 2011 it strengthened to $1 = 0.833CHF (one franc equalling $1.20). As fears about the Greek debt crisis faded the dollar strengthened slightly, but then weakened again as a result of fears over the US debt ceiling.
Due to its status as a safe haven the Swiss franc often has a retroactive value, reflected more by the weakness of the dollar and the euro than any particular strength on the part of the Swiss economy. Of course, consistent strengthening of the franc is beginning to cause problems for Swiss exporters, as trade with neighbouring countries becomes more expensive, which may see a weakening in the franc. At present, the Swiss government is still confident on the outlook for the Swiss economy, and ratings agencies seem to agree with the 'stable' AAA rating.