The “International Slag Valorisation Symposium” is a benchmark in the domain of slag engineering and zero-waste slag valorisation. It aims at contributing towards near zero-waste processing and processes and closed material loops by offering to researchers, industrial actors and entrepreneurs the opportunity to share knowledge and critically discuss the challenges and opportunities in the field of slag valorisation. To that end, specialists and/or high-level representatives of the key institutes in this field from both academia and industry are invited to give a lecture covering a specific topic in a relatively detailed way, striking a balance between scientific depth and relevance as regards industrial application in pursuit of a sustainable world. The content of the Symposium provides a rich overview of the contemporary trends in the worldwide research and innovation strategies as regards the valorisation of ferrous and non-ferrous slag, fly ash, bottom ash and numerous other high-temperature (metallurgical) residues.