This dissertation contains four articles that in different ways inform on investor behavior in international financial markets, their impact on the underlying market, and the trading strategies that they pursue. Article I studies how hedge funds herd in currency future contracts and how it is affecting the underlying market. The results indicate that hedge funds herd, and that they herd in a pattern that is consistent with them following the carry trade strategy. Hedge fund herding has an impact on the underlying market, in the direction of the herd, and the results give no indication that their herding in destabilizing. Article II examines if limits to arbitrage can help explain the returns to technical analysis strategies in the foreign e...