Space is a non-renewable resource. What happens when this resource becomes scarce and towns and cities can no longer expand? Is it possible to conceive of spatial development without expansion? Two spatially restricted cities in Europe-West Berlin at the time of the Berlin Wall from 1961 to 1989, and London, which has been enclosed by a green belt since 1958-demonstrate the consequences and imperatives of such a scenario. If both cases are understood as the consequence of spatial limitation strategies, they provide insights into the challenges as well as the potential that such restrictions present in practice. They show how spatially limited cities take a new direction in order to find their own particular form, structure, and aesthetics, and how this results in innovations in planning culture. Based on extensive map material and analyses, Limits: Space as Resource explores the spatial components of the complex question of sustainability at the urban scale, in order to contribute to a more in-depth and refined understanding of sustainable urban development.