Under Secretary Tom Ridge, the new Office of Homeland Security was created by President Bush shortly after the devastating Sept. 11, 2001 terrorist attacks. 

According to the presidential Executive Order creating it, the mission of the Office of Homeland Security is "to develop and coordinate the implementation of a comprehensive national strategy to secure the United States from terrorist threats or attacks." 

In carrying out its mission, the Office of Homeland Security coordinates the anti-terrorism efforts of over 40 federal agencies. While the exact list is classified, here is a partial list of agencies involved in homeland defense.

Policy and Goal Setting

• National Security Council - Foreign relations and activities of foreign terrorist factions
• Council of Economic Advisers - Economic response and recovery from terrorist attacks

Direct Intervention & Prevention

• Department of Defense - Provide direct military response
• Federal Bureau of Investigation - Locate and arrest terrorists inside US and coordinate with international law enforcement agencies
• State Department - Negotiate with foreign countries - preserve coalition against terrorism
• Treasury Department - Locate and freeze funds of terrorist groups
• Coast Guard - Patrol U.S. ports and waterways
• Immigration & Naturalization Service - Patrol borders, controls entry into the US by foreign nationals
• Customs Service - Locate & seize smuggled weapons, explosives, biological weapons, etc.
• Drug Enforcement Agency - Control drug trade (drug trafficking known to be a source of funding for terrorist groups)

Intelligence/Information Gathering

• Central Intelligence Agency - Gather terrorist information in foreign countries
• Federal Bureau of Investigation - Gather terrorist information inside USA
• National Security Agency - Intercept all forms of terror-related communications
• Defense Intelligence Agency - Coordinate intelligence efforts of military branches
• National Reconnaissance Office - Launch and monitor surveillance satellites 
• Special Operations Command - Gather information on terrorist locations and defenses
• US Space Command - Monitor US and Canadian airspace
• Treasury Department - Gather information on worldwide terrorist financial assets
• Securities and Exchange Commission - Detect stock trading in support of or related to terrorist groups

Preparedness & Recovery

• Federal Emergency Management Agency - train and equip local emergency service providers - coordinate all federal recover efforts
• Office for Domestic Preparedness - Train local fire and medical responders
• National Guard - Provide local security - Assist in recovery efforts
• Joint Forces Command - Reserve Units - Provide military support to local agencies
• Bureau of Alcohol, Tobacco and Firearms - Train local agencies in explosives handling
• Centers for Disease Control - Identify and isolate cases of bioterrorism-related disease
• Department of Health & Human Services - Assist local agencies respond to large-scale acts of bio-terrorism
• Environmental Protection Agency - Respond to acts of chemical warfare
• Nuclear Regulatory Agency - Protect nuclear facilities - respond to radiation-related attacks
• Agriculture Department - Protect safety of food supply, crops and livestock
• Food & Drug Administration - Provide information on and testing of bio-terrorism disease medications - monitor safety of food supply
• Transportation Department - Ensure the safety of US transportation system
• Veterans Administration - Provide backup hospital space and medical treatment
• National Infrastructure Protection Center - Protect critical computer networks