The relationship between NATO and the EU is fraught with several difficulties and has become progressively intricate since the EU has started developing its Common Security and Defense Policy, as a counterpart of NATO. The degree of complication that the US-EU relationship has achieved can seem unexpected as they have 21 common members, all members of both organizations share roughly common values and have a long history of engagement in military, economic and political arenas. This book analitically explores the relation between NATO and the EU, their modus operandi, their conception of democracy and democratization process through a study of their values,principles and the policy on which NATO and CSDP are based on. It is investigated to what extent this analysis of values translates into a decreased role for NATO in Europe and whether the emergence of the CSDP has contributed to such a decline. This work should shed some light on the current status of US-EU relationship and should be especially useful to professionals and students of IR, or anyone else who may be interested in understanding the roots of the EU and the US diverse approach in foreign policy.