Initially, the value of goods was expressed in terms of other goods, i.e. an economy based on barter between individual market participants. The obvious limitations of such a system encouraged establishing more generally accepted means of exchange at a fairly early stage in history, to set a common benchmark of value. In different economies, everything from teeth to feathers to pretty stones has served this purpose, but soon metals, in particular gold and silver, established themselves as an accepted means of payment as well as a reliable storage of value.
Originally, coins were simply minted from the preferred metal, but in stable political regimes the introduction of a paper form of governmental IOUs (I owe you) gained acceptance during the Middle Ages. Such IOUs, often introduced more successfully through force than persuasion were the basis of modern currencies.
Before World War I, most central banks supported their currencies with convertibility to gold. Although paper money could always be exchanged for gold, in reality this did not occur often, fostering the sometimes disastrous notion that there was not necessarily a need for full cover in the central reserves of the government.
At times, the ballooning supply of paper money without gold cover led to devastating inflation and resulting political instability. To protect local national interests, foreign exchange controls were increasingly introduced to prevent market forces from punishing monetary irresponsibility.
In the latter stages of World War II, the Bretton Woods agreement was reached on the initiative of the USA in July 1944. The Bretton Woods Conference rejected John Maynard Keynes suggestion for a new world reserve currency in favour of a system built on the US dollar. Other international institutions such as the IMF, the World Bank and GATT (General Agreement on Tariffs and Trade) were created in the same period as the emerging victors of WW2 searched for a way to avoid the destabilising monetary crises which led to the war. The Bretton Woods agreement resulted in a system of fixed exchange rates that partly reinstated the gold standard, fixing the US dollar at USD35/oz and fixing the other main currencies to the dollar - and was intended to be permanent.
The Bretton Woods system came under increasing pressure as national economies moved in different directions during the sixties. A number of realignments kept the system alive for a long time, but eventually Bretton Woods collapsed in the early seventies following president Nixon's suspension of the gold convertibility in August 1971. The dollar was no longer suitable as the sole international currency at a time when it was under severe pressure from increasing US budget and trade deficits.
The following decades have seen foreign exchange trading develop into the largest global market by far. Restrictions on capital flows have been removed in most countries, leaving the market forces free to adjust foreign exchange rates according to their perceived values.
But the idea of fixed exchange rates has by no means died. The EEC (European Economic Community) introduced a new system of fixed exchange rates in 1979, the European Monetary System. This attempt to fix exchange rates met with near extinction in 1992-93, when pent-up economic pressures forced devaluations of a number of weak European currencies. Nevertheless, the quest for currency stability has continued in Europe with the renewed attempt to not only fix currencies but actually replace many of them with the Euro in 2001.
The lack of sustainability in fixed foreign exchange rates gained new relevance with the events in South East Asia in the latter part of 1997, where currency after currency was devalued against the US dollar, leaving other fixed exchange rates, in particular in South America, looking very vulnerable.
But while commercial companies have had to face a much more volatile currency environment in recent years, investors and financial institutions have found a new playground. The size of foreign exchange markets now dwarfs any other investment market by a large factor. It is estimated that more than USD 3,000 billion is traded every day, far more than the world's stock and bond markets combined.