TARGET AUDIENCE: Bulk power transmission systems are operated symmetrically. When a problem occurs on a three-phase line such as a short-circuit on an individual phase, all three phases are taken out of service even though two sound phases remain and are able to function normally. Such a strategy is fundamentally inefficient: considering that, on average, 95% of faults on EHV and UHV transmission systems are single-line-to-ground faults, such a strategy is fundamental incorrect 95% of the time and is therefore wasteful of installed transmission capacity. ORIGINALITY: Asymmetric operation involves operating power transmission corridors at full capacity from a few milliseconds to a few hours even though individual three-phase lines have been weakened due to fault conditions. This book describes how asymmetric operation is implemented, how much it costs and how it can improve the reliability, economics and flexibility of electric power transmission systems. Numerous examples of asymmetric operation are provided at all major HV, EHV and UHV voltages demonstrating the very real benefits of asymmetric operation. SUBJECT MATTER: First, the underlying concepts of symmetric three-phase transmission system planning and operation are introduced. Then, asymmetric operation is presented, and its impact on system security and reliability is considered. Different implementation strategies are examined, and numerous practical examples illustrate the ease and flexibility with which such strategies can be applied in the case of either multiple- or single-line AC power transmission corridors. Finally, economic analysis quantifies the benefits of asymmetric operation.