This chapter examines key public policies at the UN and EU levels designed to ensure the social, economic, and environmental sustainability of modern societies, particularly in large urban centers and cities. The first section of the chapter explores current trends in public policy theory and methodology, with a particular focus on understanding and addressing complex, cross-sectoral issues. This includes discussions on approaches to polycrisis and wicked problems. Next, the text reviews fundamental international policies as reflected in key resolutions, conventions, and actions of the United Nations. These include the Stockholm Declaration, which emphasizes the importance of protecting the environment and integrating environmental considerations into development planning (United Nations, Report of the United Nations conference on the human environment (Stockholm, 5–16 June 1972). United Nations. https://www.un.org/en/conferences/environment/stockholm1972 , 1972). It also covers the Convention on Biological Diversity (CBD), adopted in 1992, and Agenda 21, a comprehensive action plan for sustainable development that was agreed upon at the United Nations Conference on Environment and Development (UNCED) in Rio de Janeiro in 1992. Additionally, the Framework Convention on Climate Change (UNFCCC), established at the 1992 summit as a foundation for addressing climate change issues, was later complemented by the Millennium Declaration (UN, 2000), the Paris Agreement (2015), and the Sustainable Development Goals (SDGs) within the 2030 Agenda. In addition, the chapter explores the European Union’s policies and strategic direction for green and digital transformation over the next five years. It emphasizes the need to align digital and green advancements with European values and sustainability objectives, highlighting the crucial role of the digital sector in addressing societal challenges, including education, employment, and climate action. These efforts contribute to the broader goals of the United Nations’ 2030 Agenda. Despite the introduction of significant policies and financial instruments like Next Generation EU, progress has been uneven, and key targets are at risk of being delayed. Therefore, stronger coordination, investment, and policy execution are essential to ensure Europe’s leadership in digital innovation and its commitment to sustainable development. Finally, the present chapter provides a comprehensive typology of contemporary urban models within the framework of sustainable development, critically assessing their conceptual foundations, practical implementations, and socio-spatial implications. It traces the historical evolution of the city from the classical “polis” to modern paradigms such as the Compact City, Green City, Smart City, Eco-City, Creative City, 15-Minute City, and Co-city. A critical analysis, drawing on Foucauldian concepts of biopolitics and governmentality, interrogates how smart, creative, and green cities function as instruments of population regulation and market rationality. Empirical case studies—from Bologna to Vancouver, Amsterdam, and Barcelona—illustrate the complexities, contradictions, and transformative potentials embedded in the urban future. The discussion advocates for a post-neoliberal urban vision focused on justice, democratic participation, and ecological stewardship. The chapter concludes by suggesting the use of polycrisis and wicked policy problem approaches to design sustainable policies for contemporary cities.