Central banks intervene or buy currencies to increase their value on foreign exchange markets. The world's major central banks last co-operated to support a currency in 1995, when they backed a struggling dollar. Yesterday, the US Federal Reserve, the Bank of Japan, the ECB and the Bank of England exchanged billions of dollars for euros to raise the euro's value and signal it was trading close to its bottom levels. Recently, intervention had lost favour because its effects were considered short lived. But this is the first major intervention to support the euro and states clearly that the major powers will not stand by while the currency collapses.