A method operates a drive train the is formed of an internal combustion engine, an electric motor, a transmission and a first clutch that connects the internal combustion engine to the electric motor. During an operating state for applying a current requested torque to a transmission input with the electric motor switched on and the internal combustion engine switched off, the internal combustion engine is connected into the circuit by increasing the torque applied to the drive train by the electric motor before the internal combustion engine starts, in such a way that only the current requested torque is applied to the transmission input. Excess torque is extracted from the drive train by actuating the first clutch and applying the excess torque to the internal combustion engine in order to accelerate it. The internal combustion engine is started when its starting state is reached.