In the sixth chapter of this book, we discuss system operation and connection requirements. We answer four questions. First, why pay attention to these detailed technicalities? We revisit two iconic incidents and the main lessons learned. Second, how to organize regional system operation? We explain the evolution from voluntary initiatives to formalized structures and look at the new framework to prevent, prepare for and manage electricity crises in Europe. Third, how to introduce minimum technical standards? We give an overview of the different concepts in the EU connection network codes. Fourth, how to proceed with the implementation of technical standards? We discuss four issues in the ongoing implementation of the connection network codes and the special case of energy storage. The chapter ends with a conclusion, in which we summarize our main points.