Spectroscopy in Catalysis is an introduction to the most important analytical techniques that are nowadays used in catalysis and in catalytic surface chemistry. The aim of the book is to give the reader a feeling for the type of information that characterization techniques provide about questions concerning catalysts or catalytic phenomena, in routine or more advanced applications. The title Spectroscopy in Catalysis is attractively compact, but not quite precise. The book also introduces microscopy, diffraction and temperature-programmed reaction methods, as these are important tools in the characterization of catalysts. As to applications, I have limited myself to supported metals, oxides, sulfides and metal single crystals. Zeolites, as well as techniques such as nuclear magnetic resonance and electron spin resonance, have been left out – mainly because I have little personal experience with these subjects. Catalysis would not be what it is without surface science. Hence, techniques that are applicable to study the surfaces of single crystals or metal foils used to model catalytic surfaces, have been included. The book has been written as an introductory text rather than as an exhaustive review. It is meant for students at the start of their Ph.D. projects, and also for anyone else who needs a concise introduction to catalyst characterization. Each chapter describes the physical background and principles of a technique, a few recent applications to illustrate the type of information that can be obtained, and an evaluation of possibilities and limitations. Chapter 9 contains case studies which highlight a few important catalyst systems and illustrates the power of combining techniques. The Appendix, which incorporates the surface theory of metals and details of chemical bonding at surfaces, is included to provide a better insight into the results of photoemission, vibrational spectroscopy, and thermal desorption. Finally, an important starting point is that reading the book should be enjoyable. Therefore, the book contains many illustrations, as few theoretical formulas as possible, and no mathematical derivations. I hope that the book will be useful and that it conveys some of the enthusiasm I feel for research in catalysis.