The paper examines the growing role of city networking with transnational relevance, correlating it with the supranational interest addressing the sustainable evolution of urban contexts, which seems capable of overcoming the traditional blindness of international and European law towards cities. After outlining the phenomenon in its fundamental traits, the paper focuses on the city networks endowed with greater political visibility and capacity for innovation at the international and European levels. In addition, this paper addresses the opportunities and critical issues related to the hypothesis that city networks should be more involved in supranational decision-making mechanisms, aiming to enhance the contribution of local communities to the sustainable transition.