The invention relates to a hybrid drive unit, in which for the most optimum possible synergetic use of the combustion engine drive and electromotive drive, a multi-speed clutch- and gear assembly is provided, in which both the combustion engine drive power and also the electromotive drive power is introduced into an input member of the clutch- and gear assembly. Hereby, numerous drive variants are made possible, which allow the drive machines to cooperate with each other according to requirements. The invention additionally relates to the method by which such a drive unit is operated.