As all the major traded currency pairs involve pairing with the US Dollar it's not exactly a surprise to hear that the buck is the largest traded currency in the world, but as forex traders we're more interested in how the various currency pairs compare with each other and the graphic here tells the story.
The EUR/USD pairing is undoubtedly the 800lb gorilla of the forex world, followed by the USD/JPY and some way behind by the GBP/USD. The USD/CHF is a poor fourth. However, in terms of sheer tradability, the GBPUSD is streets ahead of any of its competitors and anyone not trading that pair every day is leaving serious money on the table.