This issue of Catalysis Today presents a selection of contributions to the 12th International Symposium on the Scientific Bases for the Preparation of Heterogeneous Catalysts (PREPA12), that was held on the campus of the “Université catholique de Louvain†(UCLouvain) in Louvain-la-Neuve, Belgium, on July 8–12, 2018. This series of symposia was initiated in 1975 and occurred on a regular 4-year interval basis. Previous proceedings of these symposia have been published in Studies in Surface Science and Catalysis, and then in Catalysis Today for the PREPA11 edition. As for previous events, this 12th Symposium was made possible thanks to the organizational skills of the members of the research groups active in heterogeneous catalysis at the “Institute of Condensed Matter and Nanosciences†of UCLouvain, Belgium, and at the “Centre for Surface Chemistry and Catalysis†of KULeuven, Belgium.