This book explores the increasingly significant role of cities as actors in the European Union’s foreign policy, with a particular focus on EU-China relations. Analysing theoretical foundations, empirical data, and a survey of 745 cities, the authors provide unparalleled insights into the practices, challenges, and transformative potential of city diplomacy through its networks, partnerships, and direct engagement with global challenges. Examining approaches across cities such as Amsterdam, Barcelona, Lodz, Linz, Duisburg, Ostrów Wielkopolski, and Dietzenbach, the methodological approach captures the complexity and variety of urban diplomatic practices to explore the factors influencing city diplomacy and address critical questions central to understanding its role in contemporary international relations. Considering how cities shape and influence EU foreign policy, the authors investigate how the size of a city affects its capacity for international cooperation and how collaboration with academia and business can amplify their diplomatic outreach. Finally, the book explores the role of policy coordination between cities and higher levels of government, highlighting its importance in achieving coherent foreign policy goals and overcoming institutional barriers. Bridging the gap between academic research and policy practice, this volume offers valuable insights for scholars, practitioners, and policymakers. By highlighting the growing significance of city diplomacy, it provides a timely contribution to the fields of international relations, European studies, and paradiplomacy.