Never before in history has the amount of international trade been higher or more efficient than it is today. The fastest growing type of trade is the speculative currency trading, searching for instant profit based only on the anticipation of the variations in currency exchange rates. When currency speculation becomes an influential part of the capital flows it becomes harmful and creates instability of currency systems. Exchange rates starts to fluctuate due to the will and anticipation of speculators rather than the economic health of the country associated with the currency. This has led to recurring currency crises all over the world and an increased interest in regulatory mechanisms. One of the most discussed mechanisms proposed to handle this harmful evolution of the foreign exchange markets is the Currency Transaction Tax (CTT). The CTT stipulates a low tax (0.1 per cent) on all currency transaction to curb the incitement of short-term speculation based on a large amount of smaller transactions. The purpose of this thesis is to examine whether an implementation of a CTT is compatible with the EU treaties. This purpose consists of two research questions; whether the CTT is in conformity with the substantive law of the EU, more precisely the free movements of capital, and if the CTT is in conformity with the Economic and Monetary Union (EMU) and the exclusive power of the European System of Central Banks (ESCB) over monetary policy. Since this thesis aims to identify if the CTT is in conformity with existing legislation, the traditional doctrinal method is used for identifying and analysing potential difficulties with the CTT and to interpret these provisions in the light of ECJ case law and literature. The thesis concludes that the CTT is in conformity with the EU treaties. It does however require the full cooperation of the ESCB and ECB to achieve the objectives; to create a more stable currency market. The CTT is ready to implement.