The Muslim militant group Jemaah Islamiah, which some foreign governments suspect played a part in the deadly bombing of a Bali nightclub, is one of several radical groups in Indonesia.
Governments and some security analysts believe Jemaah Islamiah (JI) as the most likely Indonesian group to have planned the October 2002 Bali bombings, as well as more recent attacks.
The Indonesian Government has linked the group, which means "Islamic community", with Osama Bin Laden's al-Qaeda network.
JI is a shadowy group believed to want a pan-Islamic state covering Malaysia, Indonesia, Singapore and the southern Philippines island of Mindanao.
Mr Ba'asyir says he is a simple preacher
The man believed to be the group's spiritual leader, Abu Bakar Ba'asyir, has praised Osama Bin Laden as a "true Islamic warrior" but denies any links with him or with al-Qaeda.
Mr Ba'asyir is currently on trial for plotting to overthrow the Jakarta Government and turn Indonesia into an Islamic state, for which he could be imprisoned for life.
The charges relate to a series of church bombings on Christmas Eve 2000, which killed 19 people.
He has not been named as a suspect in the Bali bomb.
One of his key associates is thought to be Riduan Isamuddin, also known as Hambali, who fought the Soviets in Afghanistan.
Hambali, thought to be the brains behind the group's operations, is in hiding, with reports of his whereabouts ranging from Indonesia to Pakistan.
Evidence to link JI to the Bali bomb is circumstantial. Analysts say it is the only group with the capacity to carry out such an attack, though some believe it would still have needed outside help.
The Indonesian authorities have arrested more than 30 people with links to JI since the Bali attacks.
Malaysia and Singapore have arrested almost 100 people it says are linked to JI.
Islamic Defenders' Front (FPI)
The FPI, which has a reputation for raiding bars and nightclubs, announced in early November that it was suspending its activities indefinitely.
However the group, which has several thousand members, said it was not disbanding.
Unlike other groups it is not fighting for an Islamic state, but it does want to establish strict Sharia law.
Its supporters are concerned with local issues, acting within their communities against what they see as being against Islamic law.
Many members are young and believe that Muslims in Jakarta, and all over Indonesia, have erred from Islamic teachings.
The Islamic Defenders' Front has held anti-US demonstrations
In 2001, the group threatened to attack Westerners in retaliation for US-led bombing of Afghanistan, but the threats were not carried out.
This group emerged during the 1997 economic and financial crisis. Its leader Habib Rizieq Shihab is on trial on charges of inciting his followers to make violent raids on various social establishments.
He could face up to seven years in jail.
Although it has been accused of raiding nightclubs, analysts do not think the FPI was involved in the Bali attack. Nor have they used explosives before.
Darul Islam, which means "abode of Islam", sent volunteers to Afghanistan to help fight the US, but any links with al-Qaeda would be difficult to prove.
Darul Islam has been in Indonesia since the 1930s or 1940s, long before al-Qaeda was established.
It emerged in the aftermath of Indonesia's successful guerrilla war against the Dutch, and has fought for an Islamic state, but only within Indonesian boundaries.
It was also prominent in the 1950s, when it led rebellions in Aceh, South Sulawesi and West Java.
The paramilitary group became known for fighting a "holy war" against Christians in the Moluccan islands and central Sulawesi.
From 2000, the group, which was based in Yogyakarta in southern Java, sent thousands of men to go to the troubled regions to lead Muslim villagers against their neighbours.
12 October 2002 - Bomb at a nightclub kills about 200 people
2002 - Series of raids on nightclubs by the Islamic Defenders' Front
2001 - Laskar Jihad militants start leading attacks against Christians
2000 - Laskar Jihad militants arrive to help Muslims fight Christians
Soon after the Bali bombing, the group announced it was disbanding. But it has denied its decision was linked to the bomb.
Its commander, Jafar Umar Thalib, is on trial accused of inciting religious violence, so analysts say the decision to disband could be an attempt to avoid a prison sentence.
The group says its mission is to forge a spiritual form of jihad through preaching, not fighting. It runs a school and hospital near Ambon, in the Moluccas.
Mr Thalib fought with the Afghan Mujahideen against occupying Soviet forces. He denies any links with al-Qaeda but met Osama Bin Laden in Pakistan in 1987.
Analysts say Laskar Jihad has a domestic agenda and does not have convincing links with international networks.
It does have informal ties with some Muslim politicians, however.
In May 2002 Vice-President Hamzah Haz, who leads Indonesia's largest Muslim political party, the United Development Party (PPP), controversially visited Mr Thalib in prison.
He said he was visiting only on a humanitarian basis and was not interfering in the case. Since then, several Islamic figures have also visited, but not formally on behalf of the parties.
Some analysts believe Laskar Jihad was set up with the backing of elements in the Indonesian military.