This chapter examines the European Capitals of Culture (ECoC) initiative as a catalyst for urban knowledge sharing and collaborative development. It explores how ECoC designations mobilize a diverse range of stakeholders—including governments, cultural organizations, businesses, academia, and citizens—to co-create collaborative development based on innovation ecosystem and urban sharing organizations. Drawing on a mixed-methods approach the study analyses the mechanisms through which ECoC programming fosters creativity, decentralization, and long-term collaborative practices. Particular attention is given to participatory cultural models, the integration of digital technologies such as AI and AR/VR, and the development of interdisciplinary networks that link culture with economic, educational, and governance sectors. The chapter highlights how ECoC cities embed sustainability and legacy planning into their strategies, ensuring that the cultural momentum extends beyond the year of designation. International cooperation and cultural diplomacy are also shown to play crucial roles in addressing shared urban challenges across Europe.