Method for operating a hybrid drive train

The method involves coupling gear assembly (14) with a power transmission path to an internal combustion engine (12). The power transmission path comprises a friction clutch (16) and a gear unit (20). The gear ratio and closing of the friction clutch is laid out and the internal combustion engine is accelerated to a firing speed and the engine is started. An independent claim is included for a method for controlling unit for operating a hybrid drive train.