The following master thesis focuses on the effect of the considerable currency reform of the 20th century. Thereby, the reasons, aims and mechanisms of the reform will be discussed. The third chapter focuses on three types of currency systems and is considered as an introduction to the following theme. Here is on the fore the development of the international currency system, beginning from the gold standard to the Bretton Woods system and up to the establishment of the international currency union such as the Currency Board or the Floating exchange rates. The last two parts of the paper deal with the actual emphasis of the master thesis. The fourth chapter focuses on the historical outline of the currency policy of the 20th century as well as the motives of the conducted currency reforms. Furthermore, the international currency crises among a speculative attack on the South-East Asian currency as a part of the Asian Financial Crisis in 1997-98 are analyzed. Finally, Greece is the point of interest as well as not yet endured discussions about the eventual exit of Greece from the euro zone (“Grexit”). Moreover, historical parallels of the currency crises as well as the actual euro crisis in Greece are analyzed within the compiled comparative studies. There out, the consequences and lessons are drawn.The following paper tries to give an answer to the question, what phenomena of the historical currency crises have the actual situation in Greece in common with. Besides is to determine, what scenarios has Greece contemporary and whether the exit of Greece from the euro zone is the economically reasonable variant. In addition, the consequences of the possible exit both for Greece and European Union are estimated.