Dense, mixed-use cities are often seen as a basic prerequisite for achieving climate neutrality by the middle of the 21st century, and thus living within the constraints of the planet’s resources. The second issue of ‘Fast Forward’ takes a closer look at this proposition and discusses the consequences for our cities. It addresses vertical densification through high-rises, infill construction, land sealing, and preservation of the existing urban fabric, but also aspects of mobility, infrastructure, and digitisation – think smart cities, AI, and data centres. With contributions by Eva Herr, Christoph Ingenhoven, Liam Young, Charlie Koolhaas, Elisabeth Merk, Philipp Rode, Werner Sobek, and more.