Hydro-Que/spl acute/bec's transmission system is among the most extensive and complex transmission networks in North America. The system's design was improved over the last few years using an optimization process based on acquired experience as well as customers' expectations. Hydro-Que/spl acute/bec's transmission system is currently designed in accordance with four major guiding principles based on a successive line of defense concept designed to counter events that are increasingly more severe but also increasingly more rare. These major guiding principles are a direct reflection of the level of risk that society accepts to tolerate in relation to the costs involved by higher reliability requirements. Que/spl acute/bec's specific context, which is characterized by long transmission lines, harsh weather, and customers' heavy reliance on electricity for their heating needs, means that very high security standards must be used in the system design. To obtain a level of reliability on par with that of our neighbors' systems, however, requires more stringent criteria and standards. This paper will describe the design philosophy of Hydro-Que/spl acute/bec's power system, the underlying major guiding principles, and the defense plans designed to ensure its reliability.