Learning from the Blackouts : Transmission System Security in Competitive Electricity Markets Electricity market reform has fundamentally changed the environment for maintaining reliable and secure power supplies creating a more integrated and dynamic network environment with new real time challenges for reliable and secure transmission system operation. But despite these fundamental changes system operating rules and practices remain largely unchanged. The major blackouts of 2003 and 2004 raised important questions about the appropriateness of these arrangements. This publication presents case studies drawn from recent large scale blackouts in Europe North America and Australia. It concludes that a comprehensive integrated policy response is required to avoid preventable large scale blackouts in the future.