191 member states meet annually in regular session. Consensus has supplanted formal voting. Special or emergency sessions may be called at any time.
This has 15 members, five of them permanent members - China, France, UK, the US and the Russian Federation. The rest are elected by the General Assembly for two-year terms. It seeks peaceful resolutions to conflicts and can impose sanctions, embargoes, peacekeeping forces and military action.
Decisions require nine "yes" votes.
the Economic and Social Council 54 elected members work to encourage co-operation for development and work with non-governmental organisations.
the International Court of Justice (World Court)
This is the UN's main court and decides disputes between countries.
Headed by the Secretary General, currently Kofi Annan, this is the seat of the UN's substantive and administrative work.
Other UN branches
There are many of these, including a wide range of UN organisations, special commissions and independent agencies that are linked to the world body co-operative agreements. Among them are the World Health Organisation, the International Monetary Fund, International Labour Organisation, the World Bank, the Children's Fund (UNICEF) and the High Commissioner for Refugees (UNHCR).