The authors examine high-reliability organizations, such as aviation and nuclear power, which actively strive to minimize errors and accidents. They describe effective techniques in risk mitigation that can be employed in other large-scale systems like health care. Specifically, the authors stress the need to maintain effective and varied communication within a system. They also discuss how, in order to manage all intended and unintended consequences, decision making in complex systems must be variable, flexible, and shared. Finally, large-scale systems need to maintain strong safety cultures and norms that reinforce common organizational missions and goals.