Israel has for four years been trying to reach a deal with Hamas for the release of a young Israeli soldier who was seized during a Palestinian militant raid near the border with Gaza on 25 June 2006.
How was the soldier captured?
Gilad Shalit, then 19, was abducted by a joint force of Palestinian militants who burrowed to an Israeli army guard post on the Israeli side of the border with the southern Gaza Strip.
Two Israeli soldiers were killed during the raid near the Kerem Shalom checkpoint and three others were injured. Two Palestinian militants also died. Gilad Shalit - a tank gunner - was reported to have suffered shrapnel wounds to his hand and shoulder.
The raid was claimed by Hamas's military wing, in league with an umbrella group called the Popular Resistance Committees which includes members of Fatah, Islamic Jihad, and Hamas, and a previously unknown group calling itself the Army of Islam.
The Army of Islam later said the Israeli soldier was being held exclusively by Hamas.
The young soldier was a corporal when he was captured, but has since been promoted to the rank of sergeant.
What happened immediately after the capture?
Three days after the raid, having demanded Sgt Shalit's unconditional release, Israel launched its first ground invasion into Gaza since its unilateral withdrawal from the strip a year earlier. It also bombed Gaza's civilian infrastructure and arrested dozens of MPs from Hamas's political wing in the West Bank.
The raids were launched with the aim of freeing Sgt Shalit and preventing rocket fire which had continued from Gaza into Israel since the 2005 withdrawal.
The situation in Gaza became overshadowed by Israel's conflict with the Lebanese group Hezbollah, who seized two soldiers and killed others on 12 July 2006.
A month after Sgt Shalit's capture, the UN's top humanitarian official described Israel's military offensive in Gaza as a "disproportionate use of force". More than 100 Palestinians died and an Israeli soldier was killed during that month.
What are the captors' demands?
The captors of Gilad Shalit have issued varied conditions, all revolving around the release of some 9,000 Palestinians held in Israeli prisons, most on security grounds.
They started by demanding that Israel free all women and youths in return for news on the captive.
Talks later centred on a list of prisoners Hamas demanded be released. Neither side has given details of the list officially.
The reported numbers in question have varied over time. In November 2009, Israel's state prosecutor's office said the government was considering releasing 450 prisoners that Hamas had asked for, and another 530 to be selected by Israel under the deal under discussion.
The 450 are said to be high-value prisoners who have been convicted of lethal attacks on Israelis, although no list has been published.
Hamas's list is also said to include Marwan Bargouthi, a popular leader from Palestinian Authority President Mahmoud Abbas's Fatah party, who is widely seen as a possible successor to Mr Abbas and a figure who might bridge the divisions between Fatah and Hamas, the main Palestinian political faction.
What is Israel's position?
Israel initially refused to negotiate at all, but later entered indirect talks brokered by Egypt.
An intensive push for a deal by outgoing Prime Minister Ehud Olmert in March 2009 failed, apparently both over the list of names to be released and Israel's demand that some prisoners be deported, rather than returned to the West Bank and Gaza.
Freeing prisoners "with blood on their hands" - those who have been responsible for the deaths of Israelis - is an emotive issue in Israel.
In early 2009, Israel published two sample lists to indicate its position.
The 10 prisoners it was willing to release outside the West Bank were, in general, convicted of attacks in which at most one person was killed, or of failed attacks.
Those it refused to release were generally high-level Palestinian militant figures, some with extensive expertise in explosives, who were held responsible for killing tens of Israelis - including in some of the most notorious suicide bombings in Israel.
Talks to free Sgt Shalit broke down later that year.
Who is brokering the talks?
Egypt has been the main mediator since Sgt Shalit's capture, but in mid-2009, Egyptian President Hosni Mubarak revealed that Germany was also involved in the discussions.
The Carter Center - run by former US President Jimmy Carter, who has visited Hamas leaders - has also been involved in the transfer of letters from and to Sgt Shalit.
But the International Committee of the Red Cross, which visits prisoners of war worldwide, has consistently been refused access to ascertain Sgt Shalit's condition or to deliver letters.
Is Sgt Shalit definitely alive?
The most conclusive proof of life was received in October 2009, a video showing the captured soldier apparently in reasonable health. He held a Gaza newspaper dated Monday 14 September giving further credence to the long-held assumption that he is in Gaza. The video was delivered in exchange for the release of 20 female prisoners.
Before that, at least two letters and an audio message were received.
The first letter, received in September 2006, was released to the media in September 2009. "My health is deteriorating daily, I am especially struggling emotionally and this is causing me much depression," the letter read, although experts said they believed it had been dictated by the kidnappers.
In June 2007, Hamas released an audio recording of Shalit reading out a statement, again thought to have been dictated. He said his health was deteriorating and he was in need of an extended period in hospital.
Another letter was reportedly delivered in February 2008, but its contents have not been released.
In June 2008, a further note was transferred, through former US president Jimmy Carter's organisation, in Sgt Shalit's handwriting, saying he continued to suffer from "health and psychological difficulties" and "much depression".
Why is the issue so important?
Israel is a highly-militarised society that views itself as surrounded by hostile nations, where most parents send their sons and daughters as conscripts and continue to serve as reservists in later life.
The last time a soldier was seized in similar circumstances was in 1994, with the abduction of Nachshon Wachsman, who died during a failed rescue attempt.
Troops are meant to open fire at any abductors, even if it means injuring the soldier being abducted, under the so-called Hannibal directive. Some testimonies have suggested that, at times in the Israeli military's history, soldiers have even been advised that the death of the captured soldier is a risk worth taking to thwart an abduction.
By contrast, Ariel Sharon's government agreed to free 429 Palestinian and Lebanese prisoners in 2004 and returned the remains of 59 Lebanese, in exchange for the release of a single Israeli citizen and the bodies of three Israeli dead held in Lebanon.
When two other soldiers were seized by Lebanese fighters from the Hezbollah group in 2006, however, Mr Sharon's successor Ehud Olmert initially went along the military path, unleashing a 34-day bombardment of Lebanon in addition to a ground invasion.
But the operation failed to retrieve the two soldiers. It was not until two years later that a swap deal took place, in which the Israelis handed over five Lebanese prisoners, including a man convicted of killing a child, and the bodies of 200 Lebanese and Palestinian fighters, in exchange for the bodies of Eldad Regev and Ehud Goldwasser.
There was no confirmation that the soldiers were dead until the day of the swap.
The most famous case is missing airman Ron Arad, whose plane came down during a raid over Lebanon in 1986.
Despite a large reward and repeated contacts through third parties, Israel has never learned what became of him and a vigorous campaign for information continues to this day.