What is Article 5? The decision: On 12 September, NATO decided that, if it is determined that the attack against the United States was directed from abroad, it shall be regarded as an action covered by Article 5 of the Washington Treaty. This is the first time in the Alliance's history that Article 5 has been invoked. Article 5 of the Washington Treaty: The Parties agree that an armed attack against one or more of them in Europe or North America shall be considered an attack against them all and consequently they agree that, if such an armed attack occurs, each of them, in exercise of the right of individual or collective self-defence recognised by Article 51 of the Charter of the United Nations, will assist the Party or Parties so attacked by taking forthwith, individually and in concert with the other Parties, such action as it deems necessary, including the use of armed force, to restore and maintain the security of the North Atlantic area. Any such armed attack and all measures taken as a result thereof shall immediately be reported to the Security Council. Such measures shall be terminated when the Security Council has taken the measures necessary to restore and maintain international peace and security. NATO's Strategic Concept recognises the risks to the Alliance posed by terrorism.

What does Article 5 mean? Article 5 is at the basis of a fundamental principle of the North Atlantic Treaty Organisation. It provides that if a NATO Ally is the victim of an armed attack, each and every other member of the Alliance will consider this act of violence as an armed attack against all members and will take the actions it deems necessary to assist the Ally attacked. This is the principle of collective defence.

Article 5 and the case of the terrorist attacks against the United States: The United States has been the object of brutal terrorist attacks. It immediately consulted with the other members of the Alliance. The Alliance determined that the US had been the object of an armed attack. The Alliance therefore agreed that if it was determined that this attack was directed from abroad, it would be regarded as covered by Article 5. NATO Secretary General, Lord Robertson, subsequently informed the Secretary-General of the United Nations of the Alliance's decision. Article 5 has thus been invoked, but no determination has yet been made whether the attack against the United States was directed from abroad. If such a determination is made, each Ally will then consider what assistance it should provide. In practice, there will be consultations among the Allies. Any collective action by NATO will be decided by the North Atlantic Council. The United States can also carry out independent actions, consistent with its rights and obligations under the UN Charter. Allies can provide any form of assistance they deem necessary to respond to the situation. This assistance is not necessarily military and depends on the material resources of each country. Each individual member determines how it will contribute and will consult with the other members, bearing in mind that the ultimate aim is to "to restore and maintain the security of the North Atlantic area". By invoking Article 5, NATO members have shown their solidarity toward the United States and condemned, in the strongest possible way, the terrorist attacks against the United States on 11 September. If the conditions are met for the application of Article 5, NATO Allies will decide how to assist the United States. (Many Allies have clearly offered emergency assistance). Each Ally is obliged to assist the United States by taking forward, individually and in concert with other Allies, such action as it deems necessary. This is an individual obligation on each Ally and each Ally is responsible for determining what it deems necessary in these particular circumstances. No collective action will be taken by NATO until further consultations are held and further decisions are made by the the North Atlantic Council.