The selection and engineering of materials is a critical component in the development of a circular economy model. Which material groups (from the waste streams) play an important role in circular design solutions, and what are their properties or development trends, is revealed in this training Topic. Products must be designed to enable complete recycling of materials and novel synthesis strategies free from toxic precursors or by-products to regenerate new raw materials. The training material also provides information on which materials in Europe are considered critical and how to avoid them in circular economy business models or circular design projects.