The National Security and Homeland Security Presidential Directive (National Security Presidential Directive NSPD 51/Homeland Security Presidential Directive HSPD-20, sometimes called simply "Executive Directive 51" for short), created and signed by President of the United States George W. Bush on May 4, 2007, is a Presidential Directive which claims power to execute procedures for continuity of the federal government in the event of a "catastrophic emergency". Such an emergency is construed as "any incident, regardless of location, that results in extraordinary levels of mass casualties, damage, or disruption severely affecting the U.S. population, infrastructure, environment, economy, or government functions."