This volume of Studies in Surface Science and Catalysis contains the Proceedings of the 9th International Symposium on the Scientific Bases for the Preparation of Heterogeneous Catalysts, held on the campus of the "Universit catholique de Louvain" (UCL) in Louvain-la-Neuve, Belgium, on September 10-14, 2006. This series of symposia was initiated in 1975 on a regular 4-year interval basis. The Symposium covered the following topics: key aspects in catalysts preparation, micro- and mesoporous supports, supported metal catalysts, structured catalysts, tailored zeolites, catalysis by bases, and catalysts for fuel production. These topics served as guidelines for the sessions both in the programs of oral communications (41 contributions including 7 keynote communications – one for each topic) and poster presentations (101 contributions). In addition, the opening invited lecture addressed the question of scaling-up high-throughput experimental approaches.