The quality of telecommunication voice services has become an important issue due to the evolving and liberalized market. With the advent of new technologies, however, a diversification takes place which makes it necessary to carefully plan and observe network quality. Speech communication quality - as it is perceived by the user or customer of a service - carries a multidimensional nature, a fact which must be reflected in its assessment and prediction with quality models. In this book a new schematic is developed which classifies different entities contributing to the quality of a service. It takes into account conversational user as well as service-related contributions. Starting from this concept, perceptively relevant constituents of speech communication quality are identified. A simulation model is developed and implemented, based on physical elements of the transmission configuration. It allows the perceptively most relevant parameters to be simulated, in real time and for the conversation situation. The book gives a valuable overview on assessment needed for reliably measuring the different quality dimensions. For the planning of telephone networks, quality models are presented which aim at predicting mouth-to-ear quality as it would be perceived by a user of the system. These models are an important tool for the planner of telecommunication networks, as they allow the expected quality to be estimated in advance, even before the network has been set up. Two well-known models (the SUBMOD and the E-model) are analyzed in more detail, with an emphasis on the psychoacoustic and psychophysical backgrounds. It turns out that model predictions are satisfactory for many types of degradations, but they can still be improved especially for new types of impairments. Proposals are made for quality model enhancement and combined approaches. Due to its `handbook' character, this book is an invaluable source of background information for anyone working in the field of speech quality assessment as well as telephone network planning and operation.