The invention relates to a braking system (1) comprising an actuator unit (10), said actuator unit comprising a brake pedal (2), a pedal simulator (4), and a brake servo (12), and a main brake cylinder (20) by way of which at least one wheel brake (42, 44, 46, 48) may be actuated, said wheel brake having a braking pressure that may be predetermined, wherein the brake pedal (2) or the brake servo (12) acts on the main brake cylinder (20) to increase or decrease a braking force. According to the invention, during a first operating mode, preferably a brake-by-wire operating mode, the braking force amplifier (12), controlled by an analysis and control unit (11), generates an outside force that acts on a piston (21) of the main brake cylinder (20), wherein the actuator unit (10) comprises a first transmission device (5) that, controlled by the analysis and control unit (11), mechanically decouples the brake pedal (2) from the piston (21) of the main brake cylinder (20) as a function of predetermined criteria during the first operating mode, or couples the brake pedal (2) to the piston (21) of the main brake cylinder (20) such that the pedal force generated at the brake pedal (2) additionally acts at least partially on the piston (21) of the main brake cylinder (20).