Every day, trillions of dollars are traded in the foreign exchange market. A huge part of that isn't businesses protecting themselves from currency swings—it's speculators trying to guess where a currency's price will go next. Some of the most famous bets are carry trades. These can earn steady profits for years, then collapse in a hurry. This chapter explains how currency speculation works, from big banks to individuals using borrowed money, and why carry trades are both tempting and dangerous.