Citation: Caprari, G.; Castelli, G.; Montuori, M.; Camardelli, M.; Malvezzi, R. Digital Twin for Urban Planning in the Green Deal Era: A State of the Art and Future Perspectives. Sustainability 2022, 14, 6263. https://doi.org/10.3390/ su14106263 Academic Editors: Paola Di Biagi, Sara Basso and Alessandra Marin Received: 31 March 2022 Accepted: 18 May 2022 Published: 20 May 2022 Corrected: 11 November 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). sustainability Article Digital Twin for Urban Planning in the Green Deal Era: A State of the Art and Future Perspectives Giorgio Caprari 1, * , Giordana Castelli 2 , Marco Montuori 3 , Marialucia Camardelli 1 and Roberto Malvezzi 2 1 School of Architecture and Design, University of Camerino, 63100 Ascoli Piceno, Italy 2 Department of Engineering, ICT and Technologies for Energy and Transport (DIITET), Research National Council (CNR), 00185 Rome, Italy 3 Institute of Complex Systems (ISC), Research National Council (CNR), 00185 Rome, Italy * Correspondence: giorgio.caprari@unicam.it Abstract: This paper provides a state of the art of contemporary Digital Twins (DTs) projects for urban planning at an international level. The contribution investigates the evolution of the DT concept and contextualises this tool within the scientific-cultural debate, highlighting the interconnection between global policies and local needs/wishes. Specifically, six case studies of DTs are compared, illustrating their application, content, technological infrastructure, and priority results. The projects presented provide an overview of the existing DT typologies, focusing on the evaluative/prefigurative use and the limits/potential of the tool in light of the socio-health, climate, and environmental crises. Reflections on DT reveal, on the one hand, its potential role in supporting decision-making and participatory processes and, on the other, the potential utopian trend of data-driven planning encouraged by public–private investments in the smart city/twin city sector. In conclusion, the study underlines the innovative role of DT as a cutting-edge scientific format in the disciplinary framework but highlights that the practical use of the tool is still in an experimental research-action phase. From this theoretical-critical review, it is possible to hypothesise new research paths to implement the realism and application potential of DTs for urban planning and urban governance. Keywords: digital twin; urban planning; urban governance; tools and techniques; geospatial tech- nologies; climate action 1. Introduction: Emerging Research Questions in the Framework of Global Strategies In the scientific and cultural debate of the discipline of urbanism, the concept of the Digital Twin (DT) applied to cities, sustainable urban policy development, and governance is currently one of the most discussed and cutting-edge topics. In order to contextualise the concept of DTs, the following is a broad definition borrowed from Bolton [1], which summarises the concept of DTs as ‘... a dynamic virtual representation of a physical object or sys- tem across its lifecycle, using real-time data to enable understanding, learning and reasoning’. This virtual representation, thus defined, has been enabled by digital technological progress and, in particular, by the new data acquisition and processing technologies that, in general, refer to the field of geomatics, information technology, and the world of geo-spatial information (Geographic Information System, GIS). Within this multi-disciplinary and trans-scalar area of research, the DT for Urban Planning pursues, openly and depending on the case, some directives or warnings on the present and future of cities. Those indications are contained in technical-scientific dossiers (e.g., Intergovernmental Panel on Climate Change, IPCC, 2014 [2,3]) or in over- national strategic programmes such as the European New Green Deal [4], the Agenda for Sustainable Development and its Sustainable Development Goals (SDGs [5]), or in the New Urban Agenda. The urbanistic application of this tool, which has been experimented mainly in other disciplines, is motivated by the need to analyse urban dynamics and assess them in advance Sustainability 2022, 14, 6263. https://doi.org/10.3390/su14106263 https://www.mdpi.com/journal/sustainability