The Forex trades have no regulation by any unified body. As the currency markets deals without any intermediaries there exist several related markets dealing with several currency instruments. In other words, there is no unified US dollar rate but there are several USD rates that differ according to the bank or retail broker trading it. The differences in the rates are not big as the arbitrageurs can use them. There is a body that pretends to be a clearing mechanism of the forex – a joint venture – FxMarket Space (the Chicago Mercantile Exchange and Reuters).
There are many factors that can contribute to the forming of the exchange rates however such of them as supply and demand are the major ones. The changes in supply and demand data also cause the corresponding changes in the price of one currency against another one. The Forex market provides the most comprehensive information about the current situation in the world.