In the 21st century urbanisation has taken flight. Today, over half of the world’s population live in cities, a share that is expected to increase to almost 70% by 2050. Furthermore, economic activity is concentrated in cities and amounts to over 80% of global GDP. It is hardly a surprise that cities are at the centre of the main challenges that we must face today: cities produce 70% of all greenhouse gases and consume two thirds of the global energy supply. They are hotspots for air pollution, overcrowding and the consumption of resources, and are often the stage for segregation, unemployment and inequality.  What is more, these problems can grow exponentially if we continue with urban business as usual. In cities, what we plan, design, and build today will continue t...