The attacks left seventeen people dead, including all three gunmen. All the defendants in the trial are accused of helping organise the attacks and buying equipment, including weapons.
Most of the defendants have said they did not realise they were involved in a terrorist attack and thought it was an ordinary crime.
Three – including the only woman – are being tried in absentia after leaving to join IS.
The attacks took place from January 7-9, 2015.
They began with brothers Cherif and Said Kouachi storming the Charlie Hebdo offices, which had been unmarked and under police guard since the paper published cartoons of the prophet Mohammed several years earlier.
The brothers shot 12 people before fleeing in a stolen vehicle.
Two days later their accomplice Amedy Coulibaly killed four hostages in the Hyper Cacher supermarket while the brothers took control of a printing office just outside Paris.
All of the attackers died that day in police raids.
Coulibaly was also responsible for the death of a young police woman the previous day, but investigators took several days to work that out.
The complex network of criminals linking the three gunmen took weeks more to unpick – by which point Coulibaly's wife and two others now charged in the case had fled to Syria.
Lawyers for survivors dismissed claims by defendants that they did not know the extent of the crimes they allegedly helped to organise.
“Since 2012, terrorism capitalised on the prevailing delinquency there is around these terrorists,” said Samia Maktouf, a lawyer for one of the attack survivors.
“They are not second fiddles, they are full accomplices. You know, when you provide a weapon it’s not to go and party.”
Later in 2015, a separate network of French and Belgian fighters for Islamic State struck Paris again, this time killing 130 people in attacks at the Bataclan concert hall, the national stadium, and in bars and restaurants.
Wednesday’s trial is opening under tight security, with multiple police checks for anyone entering the main courtroom or the overflow rooms.
At nearby news stands, the latest issue of Charlie Hebdo appeared, reprinting the caricatures of the Prophet Mohammed cited by the gunmen who killed so many of the publication’s editorial staff.
“They died so that you journalists could do your jobs,” said Richard Malka, the lawyer for Charlie Hebdo.
“Let us not be afraid. Not of terrorism, not of freedom.”