The invention relates to an injector for injecting fuel into a combustion chamber of an internal combustion engine. The injector is actuated by an actuator and is connected to a fuel supply line via which fuel is supplied under system pressure. At least one injection opening can be opened or closed off by an injection valve member, which is activated by a control piston via a control chamber to which the control piston and a piston section of the injection valve member are exposed with respective pressure faces. The control piston is a valve piston of a control valve. The pressure face of the control piston and the pressure face of the piston section of the injection valve member are exposed to the control chamber at the same side. The control piston and the piston section of the injection valve member also enclose a further control chamber which is connected to a fuel return line when the control valve is open and to the fuel supply line when the control valve is closed.