Wolfgang Beltracchi, 60, is thought to be the ringleader in a plot which saw a host of well-known collectors defrauded over 44 fakes purporting to be by artists including Max Ernst, Heinrich Campendonk, Raoul Dufy and Fernand Leger, among others.
The others charged include Beltracchi's wife Helene, his sister-in-law Jeanette and her husband, Otto Schulte-Kellinghaus.
It is thought that the fakes were chosen by sourcing information on works that were known to exist but whose whereabouts was unknown.
The family had claimed that the works were heirlooms from their grandfather, the classical scholar Werner Jägers, but scientific investigation by Dr Nicholas Eastaugh, of London firm Art Access and Research, who was called in by one buyer after they became suspicious, discovered pigments not available to artists at the time the picture were supposed to have been created.
Faked labels linked to art dealers and exhibitions had also been stuck on the back of some works.
The trial is expected to last for at least a month.