More than 150 world leaders are meeting at the headquarters of the United Nations in New York to mark the opening of the 60th annual session of the UN General Assembly.
Kofi Annan has said the UN is at a "fork in the road"
The build-up to the meeting has been marred by sharp differences between member states on key issues.
The BBC News website looks at the issues under discussion.
Issue: Widespread poverty in the developing world and inequalities across the globe have prompted large-scale campaigning throughout 2005 for increased aid, debt relief and new trade agreements.
UN aim: Progress towards existing Millennium Development Goals, adopted in 2000, which include reducing poverty, improving access to education and reducing disease around the world by 2015. Additional push for countries to set aside 0.7% of gross national product for aid.
Outcome: Sixteen pages of the 35-page UN document focus on development issues, including the Millennium Development Goals. The US did not agree to the 0.7% of GNP target.
Issue: International disagreement over definition of "terrorism".
UN aim: Universal international condemnation of terror attacks.
Outcome: Undecided. US insisted on definition of terrorism including all attacks on civilians and non-combatants. Opposed by developing nations sympathetic to Palestinian armed struggle. Text left to be decided by General Assembly.
Issue: Kofi Annan proposed a new peace-building commission to assist nations emerging from war and armed conflict.
Outcome: Agreement in principle, although divisions remain over whether the new commission will report to the Security Council or to the General Assembly, where developing countries have a greater voice.
Issue: UN criticised over lack of action in Rwanda in 1994, and its slow response to the crisis in Darfur in recent years.
UN aim: Kofi Annan proposed a UN-led response to reports of genocide that places binding obligations on member states.
Outcome: Mostly approved but without legal obligations.
Issue: Widespread dissatisfaction at existing UN Human Rights Commission, which has regularly been chaired by countries with poor human rights records, such as Sudan. Countries such as China, Zimbabwe and Russia have often escaped censure.
UN aim: Establishment of a new Human Rights Council with a membership limited to countries known to respect human rights.
Outcome: Agreement over new commission, but membership criteria and details not yet finalised.
Issue: Calls for major reform of UN systems including internal management, influenced by scandals including the oil-for-food affair.
UN aim: Mr Annan, heavily criticised over his involvement in the oil-for-food issue, proposed root and branch reforms of auditing and accountability procedures within the UN.
Outcome: General approval, although Mr Annan failed to win authority to make personnel changes and re-deploy staff.
UN SECURITY COUNCIL REFORM
Issue: The make-up of the Security Council, the key decision-making body at the UN, remains based on a post-1945 formation: the US, UK, France, Russia and China are permanent members with the power of veto. Ten other places are filled on a rotating basis without veto.
UN aim: Kofi Annan backed expansion of the Security Council to 24 members, plus clear written definitions of when it is acceptable to authorise force.
Outcome: Dropped from the summit agenda. US backs expansion in principle, but only at the "right time".
DISARMAMENT AND NON-PROLIFERATION
Issue: Growth of the international small arms trade, concern over the possible spread of nuclear technology and weapons of mass destruction.
UN aim: Calls for new agreements to regulate the arms trade, re-negotiation of the ageing nuclear Non-Proliferation Treaty and focus on disarmament by existing nuclear powers.
Outcome: All references to disarmament and non-proliferation dropped from the draft summit text, labelled a "disgrace" by Mr Annan.