This document is the final report of a two-year CERTS (Consortium for Electric Reliability Technology Solutions) project studying large-scale blackouts and cascading failures of electric power transmission systems. The project is devising new methods, models and analysis tools from complex systems, criticality, probability, and power systems engineering so that the risks of large blackouts and cascading failures can be understood and mitigated from global and top-down perspectives. The work was performed by close collaboration between Oak Ridge National Laboratory and the Power Systems Engineering Research Center at the University of Wisconsin-Madison.