The subject of Physical Adsorption has enormous economic and technological value while it continues to present significant scientific challenges with prospects for further important technological developments. The literature on the subject is truly enormous. Particularly 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: -Significant development in the theory of physical adsorption; -Developments in instrumf:ntation that allow the detailed characterization of materials including microporous solids; -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. Following an incisive historical review of the subject by K.S.W. Sing, the ASI and the book focus essentially equally on theory, assessment and applications. Topics covered include: -The dramatic progress in theoretical analysis (statistical thermodynamic and quantum mechanics), fuelled by access to exponential increases in computational capabilities, and reflected in the lectures of K. Gubbins, G. Horvath, D. Nicholson and W. Rudzinsky. -The breakthroughs in experimentation, among others: high resolution adsorption, NMR of solids and of adsorbed inert gases such as 129Xe or 1~, which are described in the lectures by W.C. Conner, I. Dekany, G. Findenegg, J. Rouquerol and M.A. Springuel-Huet. -The unique aspects of transport in micropores, analysed by J. Karger, D. Ruthven and K.K. Unger.