Fatah has been increasingly divided since Yasser Arafat's death
Fatah was once the cornerstone of the Palestinian national cause and the undisputed ruling faction of the Palestinian Authority.
The movement has fallen from its position of dominance since the death of Yasser Arafat in 2004, and in 2006 lost parliamentary elections to the militant Hamas group.
In June 2007 it was effectively driven out of the Gaza Strip after violent clashes with Hamas.
Under Arafat's leadership, Fatah evolved from a resistance group into the dominant faction of the Palestine Liberation Organisation (PLO).
Now led by another of its founders, Palestinian Authority President Mahmoud Abbas, Fatah has seen its power steadily eroded by internal division and rival political groups.
The secular nationalist party has been dogged by claims of nepotism and corruption in government and critics say it is in desperate need of reform.
The Israeli authorities, meanwhile, accused armed groups associated with Fatah of attacks on Israelis and blamed the Fatah leadership.
In the early years of the Palestinian intifada (uprising) that started in late 2000, the Israeli military responded to Palestinian violence with heavy assaults that destroyed much of the PA's infrastructure in the West Bank and Gaza.
Fatah - the name is derived from the initials of the Arabic name, Harakat Tahrir Filistin, or Palestine Liberation Movement, in reverse - was founded by Arafat and a handful of close comrades in the late 1950s.
Yasser Arafat formed Fatah as a commando cell
They wanted to rally Palestinians in the diaspora in neighbouring Arab states to launch commando raids on the young Israeli state.
The group came out into the open in 1965; under Arafat's effective leadership it became the strongest and best organised of the Palestinian factions and it has remained so ever since.
Arafat took advantage of the power vacuum in the Arab states following Israel's defeat of the allied Arab armies in 1967 to cultivate greater autonomy for the Palestinian cause.
But at the same time, he was successful in raising huge sums from supportive Arab states who shared his vision of a purely Palestinian nationalist movement - and feared the influence a successful Palestinian leftist one might have on their own populations.
Armed and unarmed struggle
Arafat took over as chairman of the executive committee of the PLO in 1969, a year that Fatah is recorded to have carried out 2,432 guerrilla attacks on Israel.
Fatah leaders were forced into exile by Israel
The ejection of Palestinian fighters from Jordan during the Black September of 1970 saw Arafat's power base move to southern Lebanon.
Israel's 1982 invasion of Lebanon saw him and the Fatah leadership banished to distant Tunisia.
But the struggle was not over in the West Bank and Gaza: Arafat loyalists - the Fatah Hawks - were key players in the first Palestinian intifada which broke out in 1987.
The Oslo peace process of the 1990s brought back many of the Fatah "old guard" back to run the newly formed Palestinian Authority.
Oslo specified the creation of a large Palestinian security force, mainly to protect Israel from militant attacks under the peace accords.
Tanzim - Arafat loyalists schooled in the first intifada
The Fatah Hawks were dissolved, but in 1995 the Fatah leadership instituted its own militia, the Tanzim.
The Tanzim acted as a counterweight to the military might of the home-grown militant Islamist groups Hamas and Islamic Jihad.
It has also served as an unofficial pro-Arafat and pro-Palestinian Authority offensive force that could attack Israeli forces in the West Bank.
The Tanzim became the leading political and military force behind the al-Aqsa intifada, which broke out in 2000.
The second intifada saw a number of armed groups associated with Fatah and Tanzim emerge, most notably the al-Aqsa Martyrs' Brigades.
The brigades are neither officially recognised nor openly backed by Fatah, though members often belong to the political faction.
Marwan Barghouti led Fatah in the West Bank
One man identified as the brigades' leader was the head of Fatah in the West Bank, Marwan Barghouti, a member of the party's "new guard" who remained in the occupied territories when the PLO was in exile.
During the intifada, the al-Aqsa Martyrs' Brigades carried out numerous operations against Israeli soldiers and settlers in the West Bank and Gaza, and suicide attacks on civilians inside Israel.
Israel's responses to the intense campaign of attacks in 2002 further weakened Arafat and Fatah's authority and left the Palestinian Authority in disarray.
Much of the authority's infrastructure was destroyed, Arafat's compound in Ramallah was besieged for five weeks, and Israel captured Mr Barghouti and convicted him of murder.
With international pressure mounting, Arafat attempted to reform the PA and rein in Palestinian militants.
Fatah and Tanzim - though notably not the al-Aqsa Martyrs' Brigades - signed a declaration rejecting attacks on civilians in Israel and committing themselves to peace and co-existence.
But attacks on Israel continued, and Arafat was forced to appoint a prime minister in March 2003 after the US and Israel refused to deal directly with him.
One month after Mahmoud Abbas, Fatah's first deputy secretary, was appointed, the US published its Middle east peace plan known as the roadmap, which outlined a step-by-step timetable towards a negotiated Palestinian state.
Mahmoud Abbas backed the US roadmap peace plan
Despite a positive start, including the negotiation of a temporary ceasefire from militant groups, Mr Abbas resigned after only four months.
He accused Arafat of refusing to hand over crucial security powers to him, and reacted angrily when Fatah's Central Council refused to endorse his handling of contacts with Israel.
The ceasefire disintegrated soon afterwards, and Palestinian suicide bombings and Israeli air strikes resumed.
In late October 2004, Arafat was taken ill and flown to France for emergency treatment. He died of a mysterious blood disorder on 11 November.
Mr Abbas was confirmed as Arafat's successor as chairman of the PLO shortly afterwards and, as Fatah's candidate, won a landslide victory in the January 2005 presidential elections.
Despite what his emphatic victory may suggest, Mr Abbas inherited a party that was divided, in need of reform, and losing its popular support.
Palestinians say they have lost confidence in Fatah's old guard
Fatah has suffered from being associated with the perceived corruption and incompetence of the Palestinian Authority.
The loss of the unifying Yasser Arafat has also allowed a rift to develop between the party's "old guard" of former exiles and its "new guard", led by the jailed Marwan Barghouti.
The division became so bad after disputed party primaries last year that the "new guard" initially registered their own list of candidates for the January legislative elections.
The two reunited at the end of December, however, fearing that a divided Fatah would not be able to fight off the challenge from Hamas.
But it seems that, even united, it has been sidelined by the growing popularity of the Islamist group.
This was dramatically underlined by underlined by Hamas' election victory in 2006.
The Fatah-dominated Palestinian Authority currently governs the Palestinian-controlled areas of the West Bank. Since June 2007, it has had little sway in Gaza.
Fatah leader and PA president Mahmoud Abbas has overrun his term - it should have ended in January 2008 - drawing the legitimacy of his leadership into question.
Central to Fatah's continued importance is the fact that it is the Palestinian faction that the international community and Israel recognise and are willing to deal with directly because it is prepared to negotiate on a two-state solution.