The Fraunhofer Building Innovation Alliance has been researching new methods and products for the circular economy for many years. As part of the masterclass, the speakers provide insights into the Fraunhofer CIRCONOMY® Hub “material cycles in the construction sector”, as well as into new material developments using deconstruction materials, and new methods for sorting and processing for the reuse of recovered raw materials. Additionally, a contribution is dedicated to the identification and new innovative solutions for dealing with critical substances from the past such as wood preservatives, asbestos, or tar, that must be eliminated from the material cycle to prevent their transfer into subsequent life cycles.