There are several reasons this book was written. One was to provide a survey of all of the information obtained to date on cuprates by photoelectron spectroscopy, a technique that has been one of the more productive techniques for providing information on the electronic structure of cuprates. Thus the book serves as a review of research, but such reviews soon become dated in a rapidly moving field. Another reason was to provide a textbook, albeit of a limited nature, for persons entering the field of photoelectron spectroscopy. This aspect of the book should be useful for a longer time. We have limited our discussion to only the techniques used in photoemission on cuprates, excluding other applications of photoelectron spectroscopy, but, in fact, not much has been omitted. Finally, we hope that experienced theorists and experimentalists from fields other than photoelectron spectroscopy will learn something of the difficulties with the photoemission experiments and problems with the interpretation of the data. Photoemission data are widely quoted and we hope to provide a better understanding of the phenemona and the experimental difficulties for those who use such data in the future. In the past few years there has been much activity in the study of complex oxides, e.g., manganates, nickelates, ruthenates, often by photoelectron spectroscopy. We hope those whose interests lie with these materials rather than cuprates will find much of value in this book.