The subject of acidity and basicity has enormous economic and technological value while it continues to present significant scientific challenges with prospects for further important technological developments. Historically, technological developments in acidity/basicity have often preceded the scientific understanding of the phenomena involved, certainly in the petroleum industry, a key beneficiarry and user of the concepts of acidity. This process, however, is very expensive and less efficient than developments based on a fundamental understanding of the scientific phenomena involved. This has been recognized over the years and it explains why university, government and industrial laboratories have in the last 50 years devoted large efforts to understanding acidity (and basicity to a lesser extent) so they can gain the technological advantage. The scientific and technological literature on the subject is truly enormous. There have been some very important articles and books on the subject that have attempted to critically review many individual contributions. During the last few years there have been three developments that led us to organize the Advanced Study Institute on which this volume is based: a) Significant developments in the theory of acids and bases; b) Developments in instrumentation that allow the detailed characterization of materials including in-situ conditions relevant to industrial processes; c) The realization that closer coupling of scientific and technological pursuits can lead to greater scientific understanding and better technology. The structure of the ASI reflected the coming-together of these three factors.