The present contribution concerns the European historical tradition of private international law, departing from the first half of the xix century, focusing on the Italian and German elaborations of Nicola Rocco and Wilhelm Chaeffner. These Authors are at the origins of the well-known Mancini’s doctrine and Savigny’s doctrine. The analysis focuses on the evolution of this branch of law within the Euro-Atlantic area, contrasting civil law and common law, comparing domestic and international perspectives. Then, the study concerns the relationship between international private law and lex mercatoria in current practice, in an attempt to determine the “spatial” reach of unidroit Principles of International Commercial Contracts. Attention is also briefly devoted to the Euro-Mediterranean area, from the 1856 Paris Congress, comparing the civil law and the Arab-Islamic tradition, under the practice of granting capitulations during colonialism in the North African and Middle Eastern Countries.