By Adam Easton
BBC News, Warsaw
The increasing privatisation of war is being discussed at a Warsaw conference.
Security contractor are playing a key role in Iraq and elsewhere
Specialists from around the world will discuss the growth of private military firms in conflict zones including Iraq.
The firms are increasingly taking over roles traditionally carried out by the military during war, in a booming industry worth $100bn (£56bn) a year.
The conference has been organised by the International Committee of the Red Cross, which fears some firms do not respect international humanitarian law.
Mercenaries are still the image in many people's minds of private warfare, but private companies now provide services ranging from personal security and weapons maintenance to the interrogation of prisoners.
They have operated in more than 50 countries and been hired by everyone from the Pentagon to dictators.
In Iraq they are essential to the war effort, making up for troop shortages and doing the jobs the US military doesn't want to do.
Still largely unregulated, they have also been involved in some of the more controversial aspects of the war.
In the Abu Ghraib prisoner abuse scandal, US army investigators discovered that contractors were involved in more than a third of the proven incidents.
None of them has been prosecuted. Not quite civilians nor soldiers, they fall under a legal grey area.
Leading specialists, academics and private company representatives will attend the Warsaw conference to discuss the growth of the industry and its worrying consequences.