Today’s cities face many challenges. The ecological emergency is pushing us to reduce our carbon footprint, stop urban sprawl, and preserve resources and natural spaces. At the same time, we need enough space to meet demographic challenges, to live in social harmony, to allow for new uses and changing lifestyles. Faced with this contradictory injunction – to have more space while spreading out less – time is an unsuspected resource! Many spaces in the city are currently underused. How can we better think about our buildings, public spaces and urban projects? Bringing back to life the city’s wastelands and forgotten spaces, pooling existing infrastructures, hybridizing the uses of buildings and public spaces, anticipating future developments in urban spaces today to facilitate their transformation, reversible and evolving construction… Numerous concrete courses of action are emerging! The result of open, multi-partner research, this booklet highlights new trends and questions, illustrated by inspiring initiatives and testimonies from experts and players in the urban fabric.