GCC - a loose alliance dominated by regional power Saudi Arabia
The Gulf Co-operation Council, or GCC, is a loose political and economic alliance made up of six Gulf states.
It aims to boost economic cooperation between members and, through collective security, to guard against any threat from neighbouring states and from Islamic extremism.
The GCC was formed in May 1981 against the backdrop of the Islamic revolution in Iran and the Iraq-Iran war.
Its members - Saudi Arabia, Kuwait, the United Arab Emirates, Oman, Qatar and Bahrain - share similar political systems and a common social and cultural outlook. They are autocratic monarchies or sheikhdoms, with limited or non-existent political participation.
Collectively, GCC countries possess almost half of the world's oil reserves. Saudi Arabia is the most powerful member of the alliance.
In 1984, the GCC created an embryonic collective defence force - the Saudi-based Peninsula Shield. But the GCC has failed to expand the force; Oman's 1991 proposal to set up a 100,000-strong joint military body was turned down.
The Peninsula Shield made no attempt to deter or counter the Iraqi invasion of Kuwait that year, but was controversially deployed to Bahrain in March 2011 to bolster security during anti-government protests.
GCC members signed an intelligence-sharing pact in 2004, aimed at countering terrorism.
On the economic front, the GCC's common market came into existence early in 2008. There were plans to adopt a single currency in 2010, but these were later shelved. A customs union was declared in 2003 but has made little progress since.
GCC countries were among the first to be hit by the global economic downturn of 2008/9, but weathered the storm better than many other parts of the world, as the oil wealth of the region meant that Gulf economies were cushioned by healthy budget surpluses.
Supreme Council: The highest decision-making body is composed of the GCC heads of state. It meets once a year. The presidency of the council rotates in Arabic alphabetical order. Decisions on substantive issues require unanimous approval.
Ministerial Council: Made up of foreign ministers or other ministers, the council meets once every three months. It proposes policies and manages the implementation of decisions.
Secretariat-General: The administrative body prepares meetings and monitors the implementation of policies.
Consultative Commission: Made up of five representatives from each member state, the commission advises the Supreme Council.
Commission for the Settlement of Disputes: Formed on an ad hoc basis to seek peaceful solutions to problems among member states.
Secretary-General: Appointed by the Supreme Council for three years, renewable once. The current incumbent is Abd-al-Rahman al-Attiya, a former Qatari Foreign Ministry official.
Security is a major issue for the GCC, but finding the collective formula that satisfies all member states is a challenge. The GCC seeks to reduce its dependence on the US for security, but there is no consensus over alternative mechanisms. Members are divided over the roles of Iraq, Iran and Yemen in possible future security arrangements.
Differences have arisen over the extent and pace of political reform. The rise of militant Islam and its uneven effects throughout the region may require greater flexibility and coordination among members.
Differences also emerged over the US-led invasion of Iraq. While some GCC states opposed the action, others - including Kuwait - served as launchpads for the military campaign.
Bahrain's decision to seek a free trade deal with the US cast a shadow over the 2004 summit and caused a rift with Saudi Arabia. Some economists said the dispute threatened efforts to unify the economies of GCC members. Oman has also signed a free trade agreement with Washington.
Talks with the EU on a free trade deal began in the early 1990s, but by the end of 2010 had stalled on the issue of export duties.
The GCC's relations with Iran have for some years been strained because of Tehran's nuclear programme, though it has preferred to engage with Iran rather than adopt a confrontational stance.
Iran has extensive trade relations with most GCC member states independently, and in 2008 the organisation agreed to enter into talks on a free-trade agreement with Iran.
Yemen has long agitated for GCC membership. However, its weaker economy and its status as a republic mark it out from its neighbours.
Labour unrest in the GCC's 13 million-stong migrant workforce community has increased in recent years. Even though trade unions are banned in the GCC, the workers, many of whom come from South and East Asia, have organised strikes and protests over low wages and poor conditions.