Because of the great importance of acid catalysis in the petrochemical industry, extensive research has been carried out during the last 30 years concerning the fundamental and applied aspects of catalysis by acids. In contrast, base-catalyzed reactions have received little attention in heterogeneous catalysis. The aim of this symposium was to evaluate our knowledge of the important area of acid and base catalysis and to cover a broad range of solids, zeolite chemistry being only one aspect of heterogeneous catalysis.