Society—and, with it, architecture—faces the major paradox that a new world must be built while we no longer have the means to do so. Climate change demands entirely new approaches to building design. Rising sea levels and increasingly frequent natural disasters require a rethinking of the location and organization of human settlements. Our planet’s limited and increasingly scarce resources compel a profound reorganization of territories and the built environment.

This environment was mainly built throughout the 20th century and is largely the cause of the ecological problems we are facing today. To preserve it, and at the same time address these problems, its characteristics must be reconsidered. We must continue to use already developed areas and existing structures, rather than consume new land and demolish and replace unwanted structures.

In his stimulating essay, French architect Paul Landauer explores the question of how contaminated soil and buildings—potential or actual ruins—can be transformed into the foundations of a sustainable world. Yet, to simply redesign existing buildings will not do. We must also grapple with the technical and theoretical questions raised by the restoration of this heritage.