The landscape of supranational institutions is highly diverse, defying a single concept of globalization. Some cross-border mechanisms aim at coordination, which would streamline the movement of capital, goods, services, and persons, but could leave intact a substantial layer of local legal ordering. Other supranational instruments aspire to achieve fuller-scale harmonization, placing more pressure on national legal systems to converge. The global web of bilateral investment treaties may be viewed as settling for coordination, the European Union as increasingly seeking harmonization, and the European Convention of Human Rights as currently located in between.In the context of property law, this Article argues that, somewhat counterintuitively, the true challenge for supranationalism lies in synchronizing private law doctrines rather than public law doctrines. Although countries in their sovereign capacities may at times resist subjecting their local regulatory powers to constitutional-like supranational property norms, they are often able to employ public law strategies that establish credible systems of cross-state commitments, while still enjoying a considerable margin of deference in exercising their sovereign powers. In contrast, moving toward a global system of private law property doctrines may require a deeper commitment to fundamental changes in local ordering, implicating core cultural, social, and economic attributes of national societies.The Article identifies the challenges of devising supranational property norms for private law doctrines, such as retention of title or good faith purchase of stolen goods. As a functional matter, because such doctrines may affect an indefinite number of parties, many of whom are not tied by contract and cannot explicitly allocate the risks involved with moving across jurisdictions, the level of uniformity required to avoid frequent legal clashes is much higher than that which typifies public law settings. As a normative matter, any change in private law doctrines must trickle down to social and cultural mechanisms so that heterogeneous crowds within and across national borders would absorb it — a formidable challenge given the slow pace of cultural change
