With 20,000 power plants, 200,000 miles of high-voltage transmission lines, 60,000 substations and 3 million miles of power line, the nation’s electrical grid is perhaps the largest and most complex machine ever assembled. Yet its size and complexity make the grid vulnerable to major disruptions, as evidenced by the widespread power outage in the United States in 2003 – when the shutdown of a high-voltage power line in northern Ohio initiated a sequence of events that caused cascading blackouts that, within hours, affected more than 50 million Americans across eight states and the Canadian province of Ontario. In the years since, the interdependencies among critical and lifeline infrastructure assets have only grown.