Presidential Policy Directive 21 (PPD-21)

PPD-21, issued in February 2013, was the presidential directive that established the U.S. policy framework for critical infrastructure security and resilience: it designated the 16 critical infrastructure sectors, assigned each one a lead federal agency (a Sector Risk Management Agency), and defined key terms like "all hazards." It was formally superseded by a National Security Memorandum on Critical Infrastructure Security and Resilience issued April 30, 2024, though CISA's current sector-designation pages still reference it directly.