Luigi Lacchè =================================================================== Europa una et diversa. Concerning ius commune europaeum and common constitutional traditions Abstract In recent years, faced with the growing complexity of the process of European integration, theory, history and juridical comparison have helped shape an issue that undoubtedly shares several important assumptions. This essay will review the two principle historic dimensions of European common law: ius commune and the "common constitutional traditions". The first - which refers to the European experience from the Middle Ages to the modern era - is often cited as a "model" of free circulation of categories, interpretive techniques and management of pluralistic jurisprudence. The second is a novum ius commune, that is, an amalgam of common constitutional traditions made increasingly more evident by the jurisprudence of the European courts of justice and various institutional attempts, foremost amongst these to date the Charter of fundamental rights of the European Union. In this context, the author discusses the complex issue of 'common law', discovering therein the possibility of better understanding a una et diversa Europe while at the same time confirming the need for complete awareness of the historical importance of each judicial issue. Indeed, the future must be built on more than analogies.