Nowadays more than half of the world´s population lives in cities. Urbanization is viewed as the primary cause of many problems, but also as the primary stage for more sustainable development in the 21st century. But the increasing and ongoing urbanization changes the economic, social, environmental and political setup of cities and can have several negative impacts related to economic and social inequities and environmental damage. At the same time the global sustainability challenges intensifies. Especially cities need to become more sustainable; they need to abolish their dependence on the unsustainable management of resources like water, energy and food.