By Barry Malone

ADDIS ABABA (Reuters) - Leaders from around the continent are gathered in Ethiopia's capital for an African Union (AU) summit. Below are some questions and answers about the organisation:

WHAT ARE ITS ORIGINS?

The AU emerged from the Organisation of African Unity (OAU) which was established in 1963 with a charter signed by 32 countries in Addis Ababa. The OAU was considered a bit of an "old dictator's club" by many in Africa and was criticised for not acting against coup plotters. The AU replaced the OAU in 2002 with 51 members and said it was going to work for closer political integration among African countries. It has set about distancing itself from the OAU by often suspending coup leaders.

WHAT DOES IT DO?

It was developed along the lines of the European Union and has ten commissioners overseeing departments including political affairs, agriculture and peace and security. Its founding charter mandates it to work for "democracy, human rights and development", while it also promotes investment in the continent and sends peacekeepers to troublespots.

Its first military intervention in a member state was the May 2003 deployment in Burundi of a peacekeepers from South Africa, Ethiopia and Mozambique. When that mission ended, Burundi became a contributor to AU peacekeeping forces.

The AU also sent peacekeepers into Sudan's Darfur region in 2004 and, at its height, that force was 7,000 strong. It was replaced by a U.N. peacekeeping mission at the end of 2007.

The AU currently has 5,000 Ugandan and Burundian troops under almost constant attack in Somalia's capital Mogadishu, and is struggling to beef up that besieged force.

IS IT EFFECTIVE?

This question is debatable. The AU often has trouble mustering enough troops for its peacekeeping missions. It is also massively underfunded, with many of its desperately poor members never paying their annual dues.

But analysts say it has grown teeth in recent years, suspending countries that have suffered coups, sending envoys to mediate between governments and rebels and genuinely promoting investment. Although its AMISOM peacekeepers in Somalia are under serious pressure, they are the only thing preventing the Horn of Africa's U.N.-backed government from falling.

WHAT ABOUT THE "UNITED STATES OF AFRICA" PLAN?

This is personal mission of Libya's Muammar Gaddafi, and has been talked about at AU summits for years. Most analysts think it is a laudable vision -- but a laughable prospect -- for a continent with myriad small civil wars and rebellions to deal with. The AU was founded with the longer-term goal of total political union, and most African leaders say they support the idea in principle. But some countries, normally led by South Africa and Ethiopia, have fiercely contested discussion of the possibility and say that it would infringe on their sovereignty.

WHAT WILL HAPPEN AT THIS SUMMIT?

Africa's long-running conflicts in Sudan and Somalia and its four coups this year -- Madagascar, Guinea, Guinea Bissau and Mauritania -- will be high on the agenda. The leaders will also discuss the continent's under-developed technological infrastructure and may launch plans to improve internet access.