The core of the book is the presentation of a systematic, continuous and logical chain into the coupled total energy system (GES) of the future, which will lead to the fully sustainable use of renewable energies. Thus, unified models are proposed that are applicable to the subsystems/sectors throughout and allow the optimization of the entire GES. Appropriate algorithms and approaches are illustrated with numerous examples. This is embedded in the context of efforts to fully integrate energy generated from renewable sources into the GES. The overarching role of IT systems for secure operations has been emphasized in the book. The relevance of the correct mapping of technologies to use cases is elaborated and necessary steps derived from this are considered technically and organizationally (standardization). Special attention is paid to the didactic presentation of the material in order to present this new, difficult and complex problem "as simple as possible, but not simpler" [according to Einstein].