Even if not originally conceived of as related to cultural heritage, the common heritage of mankind (CHM) principle progressively makes its way into this field too. International norms regulating underwater cultural heritage (UCH) fit in the same evolving trend. However, they have to relate to an existing legal framework that has a completely different – and possibly opposite – primary objective. Indeed, the United Nations Convention on the Law of the Sea (UNCLOS) provided for archaeological and historical objects found at sea, prior to the adoption of an international convention specifically for UCH. Nevertheless, the related provisions of this convention have raised many doubts. The 2001 UNESCO Convention on the Protection of the Underwater Cultural Heritage would seem to intend to fill the vacuum, but it has not yet received the necessary acceptance and this surely impacts on the promotion of the UCH towards a more ‘common’ interest. This paper retraces the evolution of the protection of UCH as perceived through the prism of the CHM doctrine, wondering whether a tangential route is the best means to reconcile these two doctrines.