Five of the men are French nationals, while one is Moroccan and another Algerian.
According to prosecutors, the network's ringleader was Farid Benyettou, who attended a mosque in north-east Paris and admits encouraging several of his followers to join fighters in Iraq.
At least one dozen youths, many of them friends since childhood, are believed to have travelled to fight US-led forces in Iraq, from 2004 onwards.
Three died in a suicide bombing in Iraq, while several others were injured or arrested in Iraq and neighbouring Syria.
The recruits were allegedly sent first to Syria, from where they travelled to Iraq. Two of the men on trial were taken into custody in 2005 as they prepared to fly to Syria.
The trial dealt with mostly procedural issues as it opened. It is scheduled to end March 28.