Critical infrastructure refers to physical and cyber assets so vital to a nation or organization that their incapacitation would have a debilitating impact. This includes sectors like energy, water, transportation and communications. The document outlines growing threats to critical infrastructure from both physical attacks and cyber incidents. It notes recent attacks on energy facilities, water systems and rail networks. While governments set standards, ultimate responsibility lies with infrastructure owners to assess vulnerabilities, design security into new systems, and partner through information sharing on threats and responses.