The forex market is the largest financial market in the world. Trading in the forex is not done at one central location but is conducted between participants by phone and electronic communication networks (ECNs) in various markets around the world.
The market is open 24 hours a day in different parts of the world, from 5 p.m. EST on Sunday until 4 p.m. EST on Friday. At any point in time, there is at least one market open, and there are a few hours of overlap between one region's market closing and another opening. The international scope of currency trading means there are always traders across the globe who are making and meeting demands for a particular currency.
Currency is also needed around the world for international trade, by central banks, and global businesses. Central banks have particularly relied on foreign-exchange markets since 1971 when fixed-currency markets ceased to exist because the gold standard was dropped.1
Since that time, most international currencies have been "floated" rather than tied to the value of gold.