This chapter as an introduction to the book refers to the European Union (“EU” or “Union”) as a law-based European project created to contribute to peace, security and stability in Europe, with a focus on EU membership. First, the EU is characterised as an integration through law, emphasizing the principle of the rule of law, and a value-based Union’s identity is addressed as reflected in EU membership. Some insights on the largest EU enlargement of 2004 are provided demonstrating the interrelation between the Union’s evolving identity and the accession of new Member States. Thereafter the Union’s role in strengthening peace and security and regional stability is revealed, taking complicated and fragile international landscape into account. After more than 70 years since the establishment of the then European Coal and Steal Community peace seams to remain the underlying aim of the Union permeating all other goals—economic prosperity, social cohesion, sustainable development, scientific and technological progress, among others. The EU’s role contributing to (regional and international) peace and security is revealed in the framework of its relations with other main organisations in the field, namely, the United Nations (“UN”) and NATO, and with an emphasis of the significance of international landscape for further EU enlargement.