Actuating device operating completely or partially hydraulically on a vehicle brake system, having: - a main brake cylinder with a piston-cylinder unit having a piston and a workspace, the workspace being hydraulically connected or connectable to a storage tank and a pedal feel simulator and being mechanically connected via an actuating device, in particular a brake pedal, and the workspace being connectable via at least one normally open valve to at least one brake circuit (BK1, BK2), - at least one hydraulically operating wheel brake associated with a brake circuit (BK1, BK2), with each of which at least an own controllable switching valve is associated, with which the wheel brake can be connected to the respective brake circuit (BK1, BK2) for pressure build-up (p up) and pressure reduction (p down), in particular in brake booster operation, - a pressure supply driven by an electric motor, the piston of which is adjustable in the cylinder by means of the electric motor, - at least one valve assembly with solenoid valves for wheel-specific pressure regulation, - at least one electrical control unit (ECU, DV1-ECU, DV2-ECU) for controlling at least valves of the valve assembly and the motor of the pressure supply, - at least one controlled outlet valve, via which hydraulic medium can be discharged directly from the respective wheel brake or the brake circuit (BK1, BK2) into the storage tank, in particular during normal operation, and - a superordinate control and regulation unit (M-ECU), characterised in that - at least one electric parking brake and an electric drive motor are provided for driving at least one axle of the vehicle, and - the electric drive motor is configured to send signals to the superordinate control and regulation unit (M-ECU) and/or receive signals from the superordinate electric control and regulation unit (M-ECU), wherein the braking force of the parking brake and/or the torque of the electric drive motor is used to generate braking force, in particular in the event of failure of modules. - a main brake cylinder with a piston-cylinder unit having a piston and a workspace, the workspace being hydraulically connected or connectable to a storage tank and a pedal feel simulator and being mechanically connected via an actuating device, in particular a brake pedal, and the workspace being connectable via at least one normally open valve to at least one brake circuit (BK1, BK2), - at least one hydraulically operating wheel brake associated with a brake circuit (BK1, BK2), with each of which at least an own controllable switching valve is associated, with which the wheel brake can be connected to the respective brake circuit (BK1, BK2) for pressure build-up (p up) and pressure reduction (p down), in particular in brake booster operation, - a pressure supply driven by an electric motor, the piston of which is adjustable in the cylinder by means of the electric motor, - at least one valve assembly with solenoid valves for wheel-specific pressure regulation, - at least one electrical control unit (ECU, DV1-ECU, DV2-ECU) for controlling at least valves of the valve assembly and the motor of the pressure supply, - at least one controlled outlet valve, via which hydraulic medium can be discharged directly from the respective wheel brake or the brake circuit (BK1, BK2) into the storage tank, in particular during normal operation, and - a superordinate control and regulation unit (M-ECU), characterised in that - at least one electric parking brake and an electric drive motor are provided for driving at least one axle of the vehicle, and - the electric drive motor is configured to send signals to the superordinate control and regulation unit (M-ECU) and/or receive signals from the superordinate electric control and regulation unit (M-ECU), wherein the braking force of the parking brake and/or the torque of the electric drive motor is used to generate braking force, in particular in the event of failure of modules.