The U.S. electric power system is in the midst of a fundamental transition from being centrally planned and controlled to being dependent on competitive market forces for its expansion and operation. Unique features of electric power, including the need to match supply and demand in real time, the interconnectedness of the networks over which power flows, and the immediate propagation of disturbances throughout the system have always posed unique challenges for reliability. Today, these challenges are even greater and there is no prior experience to draw upon for guidance in relying on markets to manage the complexities of the electric power system. At the same time, the Nation s demands for electricity and reliable electric service are increasing. As the events of recent years demonstrate, the reliability of the grid and the integrity of the markets it supports are integral to the Nation's well-being.