During the course of the last few years, the team at the Ellen MacArthur Foundation have been working hard alongside city mayors and other key stakeholders to understand the opportunities that can be unlocked by applying the principles of a circular economycircular economyA systems solution framework that tackles global challenges like climate change, biodiversity loss, waste, and pollution. It is based on three principles, driven by design: eliminate waste and pollution, circulate products and materials (at their highest value), and regenerate nature. at the scale of a city. What have they found out?