A fuel injector, in particular an injection valve for fuel injection systems of internal combustion engines, has a piezoelectric actuator or magnetostrictive actuator sealed against a fuel by an actuator seal and it has a valve closing body actuatable by the actuator and working together with a valve seat face to form a tight seat. The actuator seal includes a sealing element on the inlet end and a sealing element on the injection end, both designed to be elastically deformable and frictionally engaged with an actuating sleeve. The actuator acts on valve closing body by way of the actuating sleeve, thus at least partially compensating the forces generated by the fuel pressure and acting on the actuator by way of the actuating sleeve.