In the last decades there were many calls in politics and literature for more supervision and control of world wide currency markets. These proposals were propelled by increasing exchange rate volatility and the occurrence of several financial crises. The author Alexander Zens illustrates the state of discussion regarding external intervention in foreign exchange markets. He gives evidence of capital controls being implemented in history. The famous transaction tax, which was proposed by James Tobin in the 1970s, is scrutinised in depth. Does the tax interfere with trades of speculators or hedgers, if it was deployed comprehensively? Are there consequences for companies, which manage their exchange rate exposures? The book is directed at students, economists, managers and multinational enterprises.