Method for adapting a friction coefficient of a friction clutch which is arranged in a hybrid drive train of a vehicle between an electric machine and an internal combustion engine and is activated by a clutch actuator, in which method the friction coefficient of the friction clutch is adapted by means of a torque which is transmitted by the friction clutch and is determined by means of the electric machine when the internal combustion engine is started, characterized in that the method contains the following steps: - activation of the friction clutch in order to start up the internal combustion engine in accordance with an dd torque characteristic curve of the friction clutch, which specifies the respectively transmissible clutch torque as a function of the position of the clutch actuator, in such a way that said friction clutch transmits a setpoint clutch torque which is certain to be sufficient to start up the internal combustion engine, - detection of the change in the rotational speed (dNV/dt) of the crankshaft of the internal combustion engine over time, - determination the current real actual clutch torque, which is transmitted by the friction clutch, from the change in the rotational speed of the crankshaft of the internal combustion engine over time, the moment of mass inertia of the internal combustion engine and a drag torque (M schlepp) of the internal combustion engine in accordance with the formula TE = 7*dNV/dt, where NV represents the current rotational speed of the internal combustion engine and t represents the current time, and - adaptation of the old torque characteristic curve using filter functions or incremental changes in such a way that the setpoint clutch torque corresponds to the actual clutch torque, wherein if the current real actual clutch torque is greater than the setpoint clutch torque, the friction coefficient stored in the control device must be increased, and if the determined current real actual clutch torque is smaller than the setpoint clutch torque, the control-internal friction coefficient must be reduced. - activation of the friction clutch in order to start up the internal combustion engine in accordance with an dd torque characteristic curve of the friction clutch, which specifies the respectively transmissible clutch torque as a function of the position of the clutch actuator, in such a way that said friction clutch transmits a setpoint clutch torque which is certain to be sufficient to start up the internal combustion engine, - detection of the change in the rotational speed (dNV/dt) of the crankshaft of the internal combustion engine over time, - determination the current real actual clutch torque, which is transmitted by the friction clutch, from the change in the rotational speed of the crankshaft of the internal combustion engine over time, the moment of mass inertia of the internal combustion engine and a drag torque (M schlepp) of the internal combustion engine in accordance with the formula TE = 7*dNV/dt, where NV represents the current rotational speed of the internal combustion engine and t represents the current time, and - adaptation of the old torque characteristic curve using filter functions or incremental changes in such a way that the setpoint clutch torque corresponds to the actual clutch torque, wherein if the current real actual clutch torque is greater than the setpoint clutch torque, the friction coefficient stored in the control device must be increased, and if the determined current real actual clutch torque is smaller than the setpoint clutch torque, the control-internal friction coefficient must be reduced.