The construction of a united Europe would become one of the great challenges in the post-World War II era. The founding Declaration of May 9, 1950, highlighted that world peace could not be safeguarded without creative efforts comparable to the dangers threatening it. The greatest effort would be to build a Union among countries that for centuries had lived under the constant threat of war. The construction of a supranational Europe, in which States would cede their sovereignty, is the key to this book, which develops the community Europe that would become the European Union. Successively, European States agree to pool the sectors of Coal and Steel, a Common Market, and a Community for Atomic Energy. The success of these supranational constructions will allow Europe to continue playing a leading role in the global economy and to transform, from the Maastricht Treaty, into the European Union, in which significant efforts of supranational competence attribution are still required to maintain and strengthen international action. The importance of this book lies in the meticulous documentary reconstruction of the long process that leads to the Europe of today.