Overall, a vision for the future and far-sighted urban planning Overall, to drive sustainable urban transformation forward, are key in facilitating the development of initiatives and the mayors and city administrators need to engage multisectoral implementation of solutions at the city level in a way that businesses as well as civil society and turn them into will allow the city to rise to sustainability challenges over the stakeholders. New business opportunities are emerging long term. The major challenge for the sustainable city of based on new business models from players in many sectors. tomorrow is to pool initiatives from stakeholders in order to The key factor is to pay attention to the long-term horizon: create coherence among smaller projects and so make the developing sustainable solutions, implementing recycling city function well. At different levels, the different stakeholders policies, and setting up a circular economy. are clearly identifiable: elected officials and their teams, companies, and citizens. Moreover, since most citizens are valuable stakeholders, it is important to involve them in deliberation and decision-making Each of the six cities we selected is distinguished by vision, processes. Communities and constituencies can make their good management, and urban planning. Good municipalvoices heard. In key areas of urban life, city initiatives will government should meet the needs of citizens. One of demonstrate their value across the world and benefit many the challenges is to empower cities to do more with fewer other cities. resources. Infrastructure should be modular and scalable as a city grows. Although most cities require huge sums in essential infrastructure investments, they have constrained financial resources because of the limitations of their tax bases. A good number of cities also lack qualified staff and expertise. To develop initiatives favoring innovation, cities have to support entrepreneurs and startups and encourage collaboration with private companies. Sources IMD World Competitiveness Centre Smart City Index, https:// www.imd.org/globalassets/wcc/docs/smart_city/2columns- rankings-2020.pdf United Nations, 17 Goals to Transform Our World. The Sustainable Development Goals, https://sdgs.un.org/fr/goals 24 Quélin and Smadja | HEC PARIS | SMART CITIES | The sustainable program of six leading cities | 2021