The 35 chapters in this work analyse the main urban processes and projects in the twenty-first century. The global scale, multidisciplinary nature of the research, and quality and international scope of the team of authors make this book a mandatory benchmark for urban studies. The twenty-first-century city project has been forged in a complex context, dominated by increasing metropolitanisation and influenced by three major crises within a mere quarter of a century, all centred in cities: the financial-real estate crisis, the COVID-19 crisis and the housing affordability crisis. The consequences from these include rising inequality and urban fragmentation. However, the situation involves the emergence of new global urban stakeholders from diverse backgrounds, ranging from speculative finance to the tourism sector, compelling us to undertake a renewed interpretation of the urban phenomenon. Our cities face extraordinary challenges for the future. Not only in social, physical, or morphological terms but increasingly on an environmental front too. We are thus entering a new era of regenerative cities, requiring collaboration between appropriate urban governance and the implementation of urban environmental policies that rebalance the relationship between urbanisation and the environment.