More than two years after the uprising began in Syria, the opposition remains fractious and deeply divided.
The wide variety of political groups, exiled dissidents, grassroots activists and armed militants have been unable to agree on how to overthrow President Bashar al-Assad.
Several groups, however, have tried to form coalitions to unite opposition supporters in Syria and gain international help and recognition.
Here is a guide to some of the most prominent alliances.
In November 2012, Syrian opposition factions agreed to set up a new and more inclusive leadership council at a meeting in Doha, Qatar.
It was hoped the National Coalition for Syrian Revolutionary and Opposition Forces, which includes members from within Syria and abroad, would gain widespread international recognition as the country's sole legitimate representative, become the conduit for all financial and possibly military aid, administer areas controlled by rebel forces, and plan for a post-Assad transition.
'Civil, democratic Syria'
A blueprint for the National Coalition was outlined in a document published by the veteran dissident Riad Seif, who was subsequently elected one of its two vice-presidents. His proposals were based on the Cairo conference documents agreed in July 2012, which called on revolutionary and political opposition factions to "unite under one leadership framework".
Following the Doha meeting, the National Coalition declared on its Facebook page that it was working "to aid and support the revolutionary forces struggling to overthrow the Assad regime and to transition Syria towards a democratic and pluralistic civil state".
"The coalition also plays an important role in liaising between the needs of the Syrian people and the international community," it added.
According to its website, the National Coalition is dedicated to:
The Doha meeting was a response to increasing pressure from the opposition's foreign backers to form a new alliance that superseded the Syrian National Council (SNC), which was widely viewed as ineffective, consumed by infighting and little respected on the ground. Reaction within the SNC was mixed, with some groups concerned that they would only control 22 seats on the leadership council, but the alliance's chairman George Sabra asserted at the time: "This is a serious step against the regime and a serious step towards freedom."
The National Coalition also includes members of the Local Co-ordination Committees (LCC), a network of grassroots opposition activists, as well as representatives of the local revolutionary councils. It also has the support of the rebel Supreme Military Council (SMC) of the Free Syrian Army (FSA).
However, it does not include the National Co-ordination Committee, which represents the internal political opposition groups that reject violence and want to negotiate with the government, and several militant Islamist groups fighting alongside the rebels, including the Nusra Front.
International reaction to the National Coalition was generally positive. The six member states of the Gulf Co-operation Council (GCC) were first to recognise it as "the legitimate representative" of the Syrian people, followed by France, the UK, EU and US.
In December 2012, 100 countries at the Friends of the Syrian People conference in Marrakech also recognised the coalition. Absent were Russia, China and Iran, which have backed President Assad or blocked action by the UN Security Council.
Despite its international support, the National Coalition has suffered many of the problems experienced by the SNC, on which it is still dependent operationally and organisationally, including internal divisions and outside interference.
The National Coalition's first president, Sunni cleric Moaz al-Khatib, declared that he was resigning in March 2013, complaining that foreign powers were placing too many conditions on aid to opposition and armed rebel groups, and were trying to manipulate events for their own interests.
The resignation came five days after Ghassan Hitto was elected prime minister of the National Coalition's interim government, whose creation Mr Khatib believed was premature. Mr Hitto's candidacy was backed by the Muslim Brotherhood, which dominates the SNC, and the National Coalition's secretary general, Mustafa Sabbagh, a businessman who has strong links to Qatar.
The previous month, the SNC had publicly criticised Mr Khatib for saying he would be ready to attend talks with Vice-President Farouq al-Sharaa in a third country if the Syrian government met several conditions, including the release of tens of thousands of political prisoners.
The National Coalition has also been unable to assert overall command over Syria's rebel forces, particularly jihadist groups.
It has similarly struggled to address the humanitarian crisis, in part because of a lack of funding. An Assistance Co-ordination Unit was set up, but it has struggled to carry out anything on a significant scale. The coalition has also so far failed to administer liberated areas and provide basic services and supplies.
In May 2013, a coalition of leading rebel groups issued a joint statement sharply criticising the National Coalition, accusing it of failing to fulfil its duties, and of allowing itself to be taken over by regional and international players.
The National Coalition overhauled its leadership at a conference in Istanbul in July 2013, with candidates backed by Saudi Arabia defeating those supported by Qatar in a series of elections. Ahmed Jarba, an influential tribal figure with close ties to Riyadh, was named president after he narrowly defeated Mr Sabbagh in a run-off vote.
At the same time, Mr Hitto announced his resignation as prime minister, citing an inability to form an interim government to administer so-called "liberated" zones, co-ordinating the provision basic services and supplies.
He was replaced in September by Ahmed Tomeh, a moderate Islamist and former political prisoner who is secretary general of the Damascus Declaration, a coalition of political parties, human rights groups and pro-democracy activists named after a 2005 document that demanded Syria's transformation from a "security state to a political state".
In his first speech, Mr Tomeh said he wanted to restore order and security to rebel-held areas, protect people's property, revive the economy and invest in national resources.
In September 2013, Mr Jarba parked a storm of protest within the National Coalition's leadership when he told the UN in New York that he would participate in an international conference in Geneva aimed at finding a political solution the conflict in Syria.
The US and Russia want the Syrian government and opposition to accept a solution based on the core elements of the final communique issued after the UN-backed Action Group for Syria meeting in June 2012. The communique called for a transitional government that could include officials serving under President Assad and members of the opposition.
The Syrian National Council (SNC) is a coalition of opposition groups formed in October 2011 to offer a credible alternative to the Syrian government and serving as a single point of contact for the international community.
The current president is George Sabra, a Christian and a veteran leftist dissident.
He replaced Abdelbaset Sayda, a Kurd, in November 2012, shortly before the creation of the National Coalition for Syrian Revolutionary and Opposition Forces.
Mr Sayda and his predecessor, Burhan Ghalioun, were both criticised for failing to reconcile different groups within the opposition and present a united front.
The SNC's website says it is committed to the following principles:
It has laid out plans for a transitional period which would see it:
The new Syria, the SNC states on its website, will be a "democratic, pluralistic, and civil state; a parliamentary republic with sovereignty of the people based on the principles of equal citizenship with separation of powers, smooth transfer of power, the rule of law, and the protection and guarantee of the rights of minorities".
The SNC, which is dominated by Syria's majority Sunni Muslim community, has struggled to win over Christians and members of President Assad's Alawite sect, who each make up about 10% of the population and have so far stayed loyal to the government. The council's primacy has also been challenged by the National Co-ordination Committee (NCC), an opposition bloc that still functions within Syria and is led by longstanding dissidents, some of whom are wary of the Islamists within the SNC. Several members of the SNC have also complained about its ineffectual leadership.
The SNC has also found it difficult to work with the Free Syrian Army. However, the two groups have agreed to co-ordinate their operations and the SNC has urged the international community to support the rebels.
In November 2012, US Secretary of State Hillary Clinton said the SNC could "no longer be viewed as the visible leader of the opposition" and called for an opposition leadership structure that could "speak to every segment and every geographic part of Syria".
Following the creation of the National Coalition, Mr Sabra insisted that the SNC would not be "subsumed under anybody".
"The SNC is older than this initiative or any other initiative, and it has a deep political and regional structure," he said.
In October 2013, Mr Sabra said the SNC would not attend a meeting in Geneva planned by the US and Russia to find a political solution to the conflict. He also threatened to pull out of the National Coalition.
"The Syrian National Council, which is the biggest bloc in the coalition, has taken the firm decision... not to go to Geneva, under the present circumstances," he told the AFP news agency. "This means that we will not stay in the Coalition if it goes."
Formed in June 2011, the National Co-ordination Committee (NCC) for Democratic Change is an alliance of 16 left-leaning political parties, three Kurdish political parties, and independent political and youth activists. Its chairman is the veteran left-wing opposition activist Hassan Abdul Azim, leader of the Democratic Arab Socialist Union. His deputy and spokesman abroad is Haytham Manna, a Paris-based academic and rights activist.
Unlike the Syrian National Council and the National Coalition, the NCC is open to the idea of a political settlement with the government. Its call for dialogue is conditional on a ceasefire, the withdrawal of the army from towns and cities, and the release of all political detainees.
The NCC believes the Free Syrian Army is an essential part of the revolution and plays an important role in protecting society, but rejects calls to arm it or for foreign military intervention.
NCC leaders accused the SNC and the National Coalition of being beholden to Turkey and Gulf Arab states that provide shelter, financial support and weapons to rebel groups. It also objects to what it calls the Muslim Brotherhood's domination of the exiled opposition. In turn, the SNC and National Coalition have portrayed NCC leaders as isolated and lacking support among Syrians.
In September 2012, the NNC organised the Syrian Salvation Conference, a meeting in Damascus tolerated by the authorities. A statement agreed by participants called for the following:
Afterwards, Mr Manna said regime change was inevitable. "This regime is dead in the hearts and minds of all Syrians," he explained. "There must be negotiations on a peaceful transition of power."
The Kurdish Supreme Committee was formed in July 2012 by the Democratic Union Party (PYD) and the Kurdish National Council (KNC), an alliance of 13 Kurdish parties, under the initiative of the President of Iraq's semi-autonomous Kurdistan region, Massoud Barzani.
It was hoped the committee would administer the de facto autonomous Kurdish zone created in north-eastern Syria when government forces withdrew in the summer of 2012.
However, the KNC has complained that the PYD has not honoured the power-sharing agreement. The PYD's armed wing, the Popular Protection Units (YPG), has been accused of refusing to share security responsibility in most of the towns and villages in the Kurdish area with the KNC's fighters. Parties in the KNC have also claimed that the Kurdish Supreme Committee has become a tool of the PYD.
There has led to disagreement over how Syria's Kurds should be represented at an international peace conference in Geneva proposed by the US and Russia. The US and Turkey reportedly want the KNC to be represented by the main opposition alliance, the National Coalition, which it joined in September 2013. The PYD meanwhile wants Kurds to be represented by the Kurdish Supreme Committee. And Mr Barzani is said to want the KNC to represent itself.