The proceedings of ZEOCAT 90 reflect the wide-ranging aspects of the rapidly expanding field of zeolite science and technology. The invited plenary lectures given by eminent zeolite scientists summarize current knowledge and address topical areas of zeolite research, including a contribution on the use of zeolites as membranes. The field of investigations described in the submitted articles in this volume covers a wide area of problems ranging from the influence of the synthesis process on the properties to questions of acidity, adsorption, diffusion, and catalysis. Of special interest are the newly developed applications of zeolites in the synthesis of fine chemicals, the use of zeolites for sensors and solid electrolytes, and the sophisticated zeolite-based separation processes.