The concept of quality and usability has gained importance in information and communication technology as well as in computer science. In all phases of planning, designing, implementing, and optimizing technical systems and services, quality aspects must be taken into account so that users can experience optimal quality and usability. In this book, the quality and usability of communication systems is addressed on a fundamental level. To this end, the necessary terms are first introduced, and the basics of psychophysics and psychometrics are established. Based on this, the cycle of human-oriented system development is presented. The measurement and prediction of quality and usability are then illustrated by practical examples of communication systems. In particular, systems for information transmission (telephony, VoIP, IP-TV), spoken dialog systems, and multimodal dialog systems are discussed. Finally, models for estimating quality and usability in the development phase of such systems are presented. The book is primarily aimed at readers with a technical background, for example in computer science, information technology, or electrical engineering. In addition, however, readers from linguistics and communication sciences, acoustics, sociology, human factors, and other fields of knowledge are equally addressed. It does not presuppose any special previous knowledge. This book is a translation of the original German 2nd edition Quality Engineering by Sebastian Möller, published by Springer-Verlag GmbH Germany, part of Springer Nature in 2017. The translation was done with the help of artificial intelligence (machine translation by the service DeepL.com). A subsequent human revision was done primarily in terms of content, so that the book will read stylistically differently from a conventional translation. Springer Nature works continuously to further the development of tools for the production of books and on the related technologies to support the authors.