Two parties dominate Palestinian politics: Fatah which has been at the head of the Palestinian national movement since the 1950s, and the Islamist movement, Hamas, which won the parliamentary elections in January 2006.
Full name: Reverse acronym of Harakat al-Tahrir al-Filistiniya (Palestinian Liberation Movement) meaning "conquest" in Arabic.
Origins and development: Founded by Yasser Arafat in the 1950s to promote the armed struggle to liberate all Palestine from Israeli control.
It developed into the largest Palestinian political faction and, after recognising Israel's right to exist, led efforts towards a two-state solution with Israel under the 1990s Oslo peace accords.
Fatah members formed the backbone of the Oslo-inspired administration, the Palestinian Authority (PA), especially its bureaucrats and security forces.
The party lost power in the 2006 parliamentary elections to Hamas, after Fatah officials came to be perceived as corrupt and incompetent. The shift in power heralded a period of violence on the streets of Gaza.
Attitude to Israel: PA President Mahmoud Abbas advocates restarting the peace process and is a strong critic of armed "resistance" and attacks on Israeli civilians. His goal is to establish a Palestinian state in the Israeli-occupied West Bank and Gaza Strip, with East Jerusalem as capital.
The Fatah-affiliated al-Aqsa Martyrs' Brigades has participated, along with Hamas, in an informal militant ceasefire since 2005, but conducts what it calls retaliatory attacks against Israel.
Current status: The 2006 election defeat put Fatah on the defensive and subsequent events raised fears it would try using its political influence and military power to maintain predominance. The PA's 70,000 police and security forces are mainly Fatah loyalists.
After months of factional street fighting in which hundreds of Palestinians were killed, Fatah struck a deal with Hamas to join a unity government as a junior partner.
Palestinian Authority President and Fatah leader Mahmoud Abbas dismissed the Hamas-led government in June 2007 in the wake of some of the worst fighting that resulted in the Gaza Strip being seized by the Hamas armed forces in what the movement described as a "liberation".
A new emergency cabinet has been sworn in in the West Bank, led by Prime Minister Salam Fayyad.
Full name: Acronym for Harakat al-Muqawama al-Islamiya (Islamic Resistance Movement) and means "zeal" in Arabic.
Origins and development: Palestinian branch of the Muslim Brotherhood, committed to establishing an Islamic state in the whole of what it terms Palestine (post-1948 Israel, the West Bank and Gaza).
Since its formation 1987 it has pursued a dual function: social welfare and what it calls armed resistance. This earned respect and gratitude among Palestinians suffering under Israeli occupation, but a string of suicide bombings against Israeli civilians meant it was designated a terrorist organisation by Israel, the US and the European Union.
Its 2006 landslide win thrust on Hamas the responsibility of power and international scrutiny for the first time, but the government was not recognised by Israel or the main international mediators.
Attitude to Israel: Hamas's charter uncompromisingly seeks Israel's destruction. However, Hamas's Ismail Haniya, the prime minister of the unity government until it was dissolved in June 2007, has spoken of a long-term truce with Israel if Israel withdraws from territory occupied in 1967.
The Hamas armed wing, the Izzedine al-Qassam brigades, has participated in an informal ceasefire since 2005, but claims the right to retaliate against what it calls Israeli attacks.
Current status: Designated a terrorist group by PA donors, outside funds to the Hamas-led Palestinian Authority dried up. Banks refused to handle emergency donations fearing US penalties.
After months of wrangling with Fatah, Hamas became the senior partner in a national unity government in March 2007.
But separately, it deployed a 3,000-strong shadow security force including its supporters to tackle lawlessness in Gaza. The move exacerbated tensions with pro-Fatah security agencies sparking a major show-down with Fatah.
Mr Haniya appears to be in charge in Gaza - Mr Abbas in the West Bank. The ousted prime minister insists his sacking is illegal - as is the Fayyad cabinet, which cannot get approval in the Hamas-dominated Palestinian parliament but which is to rule by decree.