We investigate the source of information advantage in inter-dealer FX trading using data on trades and counter-party identities. In liquid dollar exchange rates, information is concentrated among dealers that trade most frequently and specialize their activity in a particular rate. In cross-rates, traders that engage in triangular arbitrage are best informed. Better-informed traders are also located on larger trading floors. In cross-rates, the ability to forecast flows explains all of the advantage of the triangular arbitrageurs. In liquid dollar rates, specialist traders can forecast both order-flow and the component of exchange rate changes that is uncorrelated with flow.