This is the final report from Annex IV under the IEA Implementing Agreement on Electricity Networks Analysis, Research & Development (ENARD). The Annex has worked out a long-term perspective in the evolution of transmission system planning and operation. This is motivated by the established targets for energy system developments, which in turn are affected by economic paradigms, environmental concerns, and security of supply requirements for the well-being of citizens. The Annex work concludes that urgent action is needed to make the power system able to accommodate in a safe and economic way the dramatic changes it is required to undergo. A main message is that the “right” investment in transmission capacity, which must be stimulated, may be regarded as “overinvestment”. Transmission lines may be “necessary” even though there is a chance that they may be underutilised in parts of their lifetime. In reality, underinvestment could be more costly than overinvestment (contradictory to the motivation for deregulation; to improve efficiency and avoid overinvestment). This is necessary, taking into account the very long planning and consenting processes and accounting for the technical aspects in the regulatory and market framework.