This seminar inquires from a theoretical and cross-cultural perspective into the diverse motives and contexts where building materials are being reused in architecture. In times of resource shortage and environmental crisis, architects have to take seriously their role in minimizing the ecological footprint. At the same time, the social and architectural motives and objectives leading building materials to be reused go beyond ecological considerations. Reusing materials often arises along with a careful consideration of local building techniques. It also has implications in design practice where the available materials play a central role. After discussing the economic, ecological, social and historical values involved in the reuse of materials, the seminar engages with contemporary reuse practices in different geographical contexts such as Switzerland, Austria, China and the US.