Since the mid-20th century, the de facto world currency has been the United States dollar. According to Robert Gilpin in Global Political Economy: Understanding the International Economic Order (2001): "Somewhere between 40 and 60 percent of international financial transactions are denominated in dollars. For decades the dollar has also been the world's principal reserve currency; in 1996, the dollar accounted for approximately two-thirds of the world's foreign exchange reserves" (255).
Many of the world's currencies are pegged against the dollar. Some countries, such as Ecuador, El Salvador, and Panama, have gone even further and eliminated their own currency (see dollarization) in favor of the United States dollar. The dollar continues to dominate global currency reserves, with 63.9% held in dollars, as compared to 26.5% held in euros (see Reserve Currency).
Since 1999, the dollar's dominance has begun to be eroded by the euro, which represents a larger size economy, and has the prospect of more countries adopting the euro as their national currency. The euro inherited the status of a major reserve currency from the German Mark (DM), and since then its contribution to official reserves has risen as banks seek to diversify their reserves and trade in the eurozone continues to expand.
As with the dollar, quite a few of the world's currencies are pegged against the euro. They are usually Eastern European currencies like the Estonian kroon and the Bulgarian lev, plus several west African currencies like the Cape Verdean escudo and the CFA franc. Other European countries, while not being EU members, have adopted the euro due to currency unions with member states, or by unilaterally superseding their own currencies: Andorra, Monaco, Montenegro, San Marino, and Vatican City.
As of December 2006[update], the euro surpassed the dollar in the combined value of cash in circulation. The value of euro notes in circulation has risen to more than €610 billion, equivalent to US$800 billion at the exchange rates at the time (today equivalent to circa US$968 billion).
Spanish dollar: 17th-19th centuries
In the 17th and 18th century, the use of silver Spanish dollars or "pieces of eight" spread from the Spanish territories in the Americas westwards to Asia and eastwards to Europe forming the first ever worldwide currency. Spain's political supremacy on the world stage, the importance of Spanish commercial routes across the Atlantic and the Pacific, and the coin's quality and purity of silver helped it become internationally accepted for over two centuries. It was legal tender in Spain's Pacific territories of the Philippines, Micronesia, Guam and the Caroline Islands and later in China and other Southeast Asian countries until the mid 19th century. In the Americas it was legal tender in all of South and Central America (except Brazil) as well as in the U.S. and Canada until the mid-19th century. In Europe the Spanish dollar was legal tender in the Iberian Peninsula, in most of Italy including: Milan, the Kingdom of Naples, Sicily and Sardinia, as well as in the Franche-Comté (France), and in the Spanish Netherlands. It was also used in other European states including the Austrian Habsburg territories.
19th - 20th centuries
Prior to and during most of the 1800s, international trade was denominated in terms of currencies that represented weights of gold. Most national currencies at the time were in essence merely different ways of measuring gold weights (much as the yard and the meter both measure length and are related by a constant conversion factor). Hence some assert that gold was the world's first global currency. The emerging collapse of the international gold standard around the time of World War I had significant implications for global trade.
In the period following the Bretton Woods Conference of 1944, exchange rates around the world were pegged against the United States dollar, which could be exchanged for a fixed amount of gold. This reinforced the dominance of the US dollar as a global currency.
Since the collapse of the fixed exchange rate regime and the gold standard and the institution of floating exchange rates following the Smithsonian Agreement in 1971, most currencies around the world have no longer been pegged against the United States dollar. However, as the United States remained the world's preeminent economic superpower, most international transactions continued to be conducted with the United States dollar, and it has remained the de facto world currency.
Only two serious challengers to the status of the United States dollar as a world currency have arisen. During the 1980s, the Japanese yen became increasingly used as an international currency, but that usage diminished with the Japanese recession in the 1990s. More recently, the euro has increasingly competed with the United States dollar in usage in international finance.