<p>Cities are no longer confined to the role of administrative units; they increasingly operate as diplomatic actors in global politics. This article investigates how urban centers project soft power and exercise agency beyond the traditional authority of nation-states. Drawing on a Hybrid Theoretical Framework that combines urban soft power, the political economy of city diplomacy, and the world society approach, the study examines five strategically selected cases—New York, Barcelona, Istanbul, Shanghai, and Tehran—chosen to reflect variation in geography, governance systems, and municipal autonomy. Methodologically, the research adopts a qualitative comparative design. Policy documents, international reports, and municipal initiatives were coded along four analytical dimensions: resources, reputation, representation, and structural positioning. This approach allows for systematic comparison while remaining sensitive to each city’s political and institutional context. The findings point to three broad patterns of city diplomacy. First, cities with high autonomy (New York, Barcelona) mobilize resources and reputational capital to lead global networks such as C40 and UCLG. Second, cities under centralized regimes (Shanghai, Tehran) engage internationally but primarily as extensions of national strategies, limiting their independent influence. Third, Istanbul illustrates a hybrid pathway, advancing cultural and symbolic diplomacy while constrained by strong national oversight. Overall, the study argues that sovereignty is being rescaled: municipal diplomacy does not replace state authority but complements and sometimes challenges it. Theoretically, this research demonstrates the value of a hybrid framework for analyzing subnational diplomacy. Practically, it highlights the role of cities as crucial partners in advancing Sustainable Development Goal 11, particularly in promoting inclusive, resilient, and globally connected urban communities.</p>