For every ten humans, seven live in a city. There are megalopolises on every continent. Everywhere constructions sprawl and homogenise the landscape, rural worlds disappear, lifestyles are standardized and yet inequalities increase. The spread of urbanisation is heating the planet, destroying biodiversity, and making us even more vulnerable to climate change. But cities are also our common good. They are the sites of wealth creation, innovation, culture, solidarity, and resilience. Their bustling crowds and abundant attractions are fascinating, but overshadow another reality: the myriad of small and medium size towns that make up most of the urban world today. Particularly those of so-called developing countries, whose "low technologies" have a much smaller impact on the planet's future than globalised metropolises. To explore these urban worlds, the authors of this Atlas have shed light on several heterogenous fields. From classic sources such as international organisations and networks of cities, to the new range of resources provided by digital technology, they have looked at different levels and broken away from ordinary territorial spatialization. This Atlas provides an unprecedented perspective on our urbanized world.