A fuel injector (1), particularly an injection valve for fuel-injection systems of internal combustion engines, has a piezoelectric or magnetostrictive actuator (16) that is arranged in a valve housing (2) and is sealed off from a fuel by an actuator housing (15), and a valve-closure member (7) which is operable by the actuator (16) with the aid of a valve needle (6) and which cooperates with a valve-seat surface (5) to form a sealing seat. The valve housing (2) and the actuator housing (15) have cut-outs (38, 39) adjoining one another, and the valve housing (2) is joined to the actuator housing (15) in an edge area of the cut-outs (38, 39). In this manner, a feed-through opening (41) is formed which is sealed off from the fuel. The feed-through opening (41) is filled with a filler element (43) by which at least one electrical supply line (37) of the actuator (16) is fixed in position in the feed-through opening (41).