What is density? This question is the starting point of an investigation into the nature of density in the contemporary urban environment. In analysing projects located throughout Europe, the research proposes that density is not about volumetric exploitation, but based on the interaction between three elements: agents, fluxes, and territory. This book documents the findings, detailing individual buildings, cataloguing specific urban forms, and drawing conclusions as to performance and quality, also in an ecological sense. It also offers a case study concerning the former site of the Renault factory in Paris, examining how an experimental opportunity can lead to a vibrant piece of city.