This book explains how member states of the EU confer powers to the Union through the founding treaties and the legal frame applicable to the UnionтАЩs institutions, and the rules that apply to their functioning and the legal review of their action. It reviews the main fields of action of the EU тАУ the internal market, area of freedom, security and justice, external action тАУ and how law is shaping them. The interaction between the EU and its member states is also explained.