The euro and the United States dollar

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 favour 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.[1]
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, Kosovo, 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).[