This is the problem: how can legal history be of help to establish a dialogue and to create a synergy between two legal systems which are different and in some measure in competition, i.e. on one hand the civil law system and on the other the common law system? Can legal history contribute to overcome the historical and cultural barriers that had been created between these two legal systems over the centuries, after their separation during the Middle Ages, allowing now – despite the differences – the construction of a productive dialogue? Furthermore, can legal history help to trace the lines of evolution of a “Global Law”, allowing us to control its development on the basis of the solid foundations provided by the legal science of the past and of the present? The aim of the paper is to find an answer to these questions and to demonstrate that legal history is not only useful to understand present-day law, but also necessary to control the future developments of law’s life. In particular, attention will be paid to an element situated at a deeper level, that is legal logic, which is shared by both systems, being based on a remote past which is common to both civil law and common law jurists.