By Martin Asser
BBC News website
The four Western hostages released within the last week are among at least 280 foreigners and thousands of Iraqis who have been taken hostage since the US-led invasion of Iraq in 2003.
The fate of about 90 foreign hostages remains unknown
Abductions of foreigners are usually motivated by politics - calling for the withdrawal of foreign forces or prisoner releases - while Iraqis are usually ransomed for money.
Some nationalities - from less influential or economically developed parts of the world - have simply been executed by their abductors to deter others from coming to Iraq.
US freelance reporter Jill Carroll was released on 30 March 2006, ending an ordeal that began in west Baghdad on 7 January.
Exactly seven days earlier Briton Norman Kember and Canadians James Loney and Harmeet Singh Sooden were released, having been seized on 26 November 2005.
Their fellow aid worker Tom Fox shared the fate of about 50 other foreign hostages - to be murdered by their captors. The US citizen - was found handcuffed and shot dead on a rubbish dump in west Baghdad on 7 March.
In all, about 140 of the foreign hostages abducted in Iraq have been released or managed to escape - while the fate of the other 90 remains unknown.
Mr Kember and his colleagues worked for Christian Peacemaker Teams (CPT), a humanitarian organisation that operates in North and South America and the Middle East.
CPT's overtly Christian title was considered possibly relevant to their capture, given the professed extremist Islamic agenda of the kidnappers - but they were probably seized because they lacked the heavily armed "close protection" employed by most foreigners in Iraq.
The phenomenon of hostage-taking in Iraq has ebbed and flowed in the public consciousness over the last three years.
The most horrific feature has been the publication of videos, filmed by various insurgent groups, showing the hostages shackled, in US-style orange prison jumpsuits - sometimes pleading for their lives.
Occasionally - thankfully not in the most recent cases - the moment of death, either by shooting or beheading, was also filmed and broadcast on the internet.
The CPT four were on a mission of solidarity with Iraqis
It may be that the killers stopped such macabre displays after the leading Islamist militant figure Ayman al-Zawahiri apparently said the practice was counterproductive - alienating ordinary Muslims.
It is also true that fewer foreigners have been kidnapped in recent months, although the number of Iraqis appears to have risen to appalling levels - 30 abductions a day by a conservative estimate.
The problem is a constant reminder of the instability of Iraq, where foreign forces and Iraqi police alike are barely able to protect themselves, let alone the general public.
Reports of kidnappings for ransom by criminal gangs began to emerge soon after the overthrow of Saddam Hussein in April 2003.
In the late summer of 2003, many middle class Iraqis kept their children at home and stopped going out at night for fear of abduction. Doctors and other professionals were particularly targeted.
More than 5,000 Iraqis are estimated to have been kidnapped since then.
The era of foreigner kidnappings began in April 2004 - during the US-led military onslaught on Falluja - when 43 foreigners were grabbed.
Hostages Simona Pari and Simona Torretta were released in 2004
The first to be killed was the Italian security contractor Fabrizio Quattrocchi, who was shot in the head on 14 April.
A video showing the beheading of American businessman Nick Berg was released on 11 May 2004 by a group reportedly led by Abu Musab al-Zarqawi, who heads al-Qaeda in Iraq.
Other gruesome videos followed.
In all 87 foreigners were seized between July and September 2004 - 22 of whom were killed, 34 were set free or escaped, but many whose fate remains unknown.
In the ensuing months some large ransoms have been paid to kidnappers (German archaeologist Susanne Osthoff was released allegedly after the payment of $5m).
But most governments have discouraged such payments - arguing that the result would be more kidnappings - although this stance has been criticised by some relatives of hostages.
No scruple or restraint seems to have checked the kidnappings - it is just one of many weapons in the insurgents' armoury against the US and its allies in Iraq.
One of their victims was Margaret Hassan, the highly respected director of Care International - a Briton married to an Iraqi who had spent the previous 25 years fighting tirelessly against poverty in Iraq.
The Egyptian ambassador-designate to Iraq was killed in July 2005, the same month that Algerian government confirmed the deaths of two of its top diplomats in Iraq.
Another Briton, Ken Bigley was killed despite a worldwide publicity campaign and pleas from politicians and religious figures alike transmitted by Arabic television.
More than any other security threat in Iraq - somewhere bursting with security threats - it is the ruthlessness of the kidnappers that has emptied the country of all but the best-protected foreigners.
A result of that, one the insurgents would no doubt approve of, has been to deal a deadly blow to efforts to rebuild the country.