Homeland Security Presidential Directive 7

Homeland Security Presidential Directive 7establishes a national policy for Federal departments and agencies to identify and prioritize critical infrastructure and to protect them from terrorist attacks. The directive defines relevant terms and delivers 31 policy statements. These policy statements define what the directive covers and the roles various federal, state, and local agencies will play in carrying it out.

http://www.dhs.gov/xabout/laws/gc_1214597989952.shtm