The electricity world is rapidly changing. On one side, renewable energy sources (RES) are being more and more massively installed everywhere. Due to the variable behaviour of a good share of them, reserve needs are increasing. So, it would be good to extend as much as possible the number of subjects enabled to provide ancillary services and participate in real-time energy markets. On the other hand, distribution networks are becoming active and a steadily higher number of distributed resources are being deployed, hence the opportunity to enable such resources to provide system services. However, in order to do so, the grid operators (transmission system operator (TSO) and distribution system operator (DSO)) should be able to coordinate their actions. This theme was the object of the SmartNet Horizon 2020 project, which constitutes the background for the material presented in the present book. However, this book, yet illustrating material and investigations derived from the SmartNet project activities, has a different aim and scope: to provide the reader with a theoretically solid background to deal in detail with architectures of real-time services markets.