Decentralization has actively engaged various fields of sociology, economy, and governance in the development of urban regions and territories. As a multifaceted strategy, decentralization contributes to enrich our understanding of national and international forces, power struggles, economic factors, and their impacts on the built environment. To frame the discourse of decentralization on urban development, three institutions of ENSAG Université Grenoble Alpes, Politecnico di Milano, and the Delft University of Technology closely collaborated to organize three conferences in Grenoble, Milan, and Delft, respectively. They called scholarly attention re-thinking of urban and regional planning of the twentieth century through the lens of decentralization’s values and ideologies. These three conferences laid out how decentralization and its evolution engaged with the field of planning, and in turn, affected urban transformation and regional development worldwide. Focusing on the role of decentralization in urban and regional planning, these scholarly events offered an innovative perspective on research on planning history. This report, therefore, reflects upon the discussions took place at these three conferences to outline the diversity of perspectives on decentralization and its role in urban and regional planning in the past, present, and future.@en