In this book, the background, state of research, and own contributions to the assessment and prediction of talker quality that is constituted in voice perception and in dialog are presented. Starting from theories and empirical findings from human interaction, major results and approaches are transferred to the domain of human-computer interaction. The main subject of this book is to contribute to the evaluation of spoken interaction in both humans and between human and computer, and in particular to the quality subsequently attributed to the speaking system or person, based on the listening and interactive experience.