Although humans spend about a third of their lives sleeping, many uncertainties surrounding the phenomenon of sleep still exist. Engaging with this topic seems to be of great importance, as many questions related to sleep remain unclear or even unanswered to this day. For example, there is still some ambiguity regarding the actual function of sleep and the individual sleep stages, as well as their effects on the waking state. This book addresses the extent to which the waking process influences sleep quality. It presents the fundamentals of sleep and its functions. The waking process and the influencing factors that enable a refreshing awakening are described. Based on scientific findings, the impact of the waking stage on the assessment of sleep and wake quality is demonstrated.