This book is intended to present for the first time experimental methods to measure equilibria states of pure and mixed gases being adsorbed on the surface of solid materials. It has been written for engineers and scientists from industry and academia who are interested in adsorption-based gas separation processes and/or in using gas adsorption for characterization of the porosity of solid materials. Traditional and new measurement methods for gas adsorption equilibria are presented in Chaps. 2-6 and elucidated by quite a number of experimental data sets, most of them having been measured in the authors' laboratories. Special emphasis is given to uncertainties of data and pros and cons of all measurement methods are offered. Also the basic concepts underlying interpretation of measurements and calculations of adsorbed masses from measurement signals, are discussed in Chap. 1. The authors state that in publishing this book they "hope to contribute to... the development of effective and reliable methods to measure pure gas and gas mixture adsorption equilibria; preventing young (and old) experimenters from doing all the mistakes we have done during our laboratory work*) ; making experimental gas adsorption data measured today in many laboratories more easily comparable to each other, as methods and procedures should become more and more similar and possibly also will be standardized (IUPAC) in the years to come. ".