The German parliament has voted to set up a committee to examine claims that German intelligence agents helped the US during the 2003 war in Iraq.
The agents allegedly picked out bombing targets in Baghdad
While the German government was expressing opposition to the conflict, agents are said to have helped US planners select targets in Baghdad.
They are also said to have co-operated with them in illegal kidnappings.
The government has tried to avoid the inquiry, arguing that it could compromise the intelligence service.
German Foreign Minister Frank-Walter Steinmeier has dismissed claims that agents of the German intelligence service, the BND, had helped the US military to select bombing targets.
He said they had remained in Baghdad during the hostilities merely to keep the government in Berlin informed.
Questions for ministers
The role of German officials in interrogating German citizens held prisoner in Syria and Guantanamo Bay will also be investigated.
The inquiry will also look at the case of German citizen Khaled al-Masri, who claims he was kidnapped in 2003 while on holiday in Macedonia and flown to Afghanistan, where he was held for five months and mistreated by the CIA.
Former Chancellor Gerhard Schroeder and former Foreign Minister Joschka Fischer will be among the witnesses.
Mr Steinmeier - who was Mr Schroeder's chief of staff at the time - will also face questions.
The BBC's Ray Furlong in Berlin says it is not clear quite how much of a grilling they will get. The committee of inquiry has eight members from the governing coalition - and just three from opposition parties.