Hezbollah - or the Party of God - is a powerful political and military organisation of Shia Muslims in Lebanon. It emerged with financial backing from Iran in the early 1980s and began a struggle to drive Israeli troops from Lebanon.
In May 2000 this aim was achieved, thanks largely to the success of the party's military arm, the Islamic Resistance.
In return, the movement, which represents Lebanon's Shia Muslims - the country's single largest community - won the respect of most Lebanese.
It now has an important presence in the Lebanese parliament and has built broad support by providing social services and health care. It also has an influential TV station, al-Manar.
But, it still has a militia that refuses to demilitarise, despite UN resolution 1559, passed in 2004, which called for the disarming of militias as well as the withdrawal of foreign (i.e about 14,000 Syrian) forces from Lebanon.
As long ago as 2000, after Israel's withdrawal, Hezbollah was under pressure to integrate its forces into the Lebanese army and focus on its political and social operations.
But, while it capitalised on its political gains, it continued to describe itself as a force of resistance not only for Lebanon, but for the region.
The Islamic Resistance is still active on the Israel-Lebanon border. Tension is focused on an area known as the Shebaa Farms, although clashes with Israeli troops occur elsewhere.
Hezbollah, with broad Lebanese political support, says the Shebaa Farms area is occupied Lebanese territory - but Israel, backed by the UN, says the farms are on the Syrian side of the border and so are part of the Golan Heights, which Israel has occupied since 1967.
Another casus belli cited by Hezbollah is the continued detention of prisoners from Lebanon in Israeli jails.
The movement long operated with neighbouring Syria's blessing, protecting its interests in Lebanon and serving as a card for Damascus to play in its own confrontation with Israel over the occupation of the Golan Heights.
But the withdrawal of Syrian troops in Lebanon last year - following huge anti-Syrian protests in the wake of Lebanese ex-Prime Minister Rafik Hariri's assassination - changed the balance of power.
Hezbollah became the most powerful military force in Lebanon in its own right and increased its political clout, gaining a seat in the Lebanese cabinet.
Analysts say Hezbollah has adopted a cautious policy since the Hariri assassination crisis erupted on 14 February 2005 - an event widely blamed on Syria, but which Damascus has vigorously denied.
Hezbollah leaders have continued to profess its support for Syria, while not criticising the Lebanese opposition. They have also stressed Lebanese unity by arguing against "Western interference" in the country.
Hezbollah was conceived in 1982 by a group of Muslim clerics after the Israeli invasion of Lebanon.
It was close to a contingent of some 2,000 Iranian Revolutionary guards, based in Lebanon's Bekaa Valley, which had been sent to the country to aid the resistance against Israel.
Hezbollah was formed primarily to offer resistance to the Israeli occupation.
It also dreamed of transforming Lebanon's multi-confessional state into an Iranian-style Islamic state, although this idea was later abandoned in favour of a more inclusive approach that has survived to this day.
The party's rhetoric calls for the destruction of the state of Israel. It regards the whole of Palestine as occupied Muslim land and it argues that Israel has no right to exist.
The party was long supported by Iran, which provided it with arms and money.
Passionate and demanding
Hezbollah also adopted the tactic of taking Western hostages, through a number of freelance hostage taking cells.
In 1983, militants who went on to join Hezbollah ranks carried out a suicide bombing attack that killed 241 US marines in Beirut.
Hezbollah has always sought to further an Islamic way of life. In the early days, its leaders imposed strict codes of Islamic behaviour on towns and villages in the south of the country - a move that was not universally popular with the region's citizens.
But the party emphasises that its Islamic vision should not be interpreted as an intention to impose an Islamic society on the Lebanese.