Abstract: An internal combustion engine fuel injector having a selectively openable nozzle (10) through which a fuel is delivered to the combustion chamber of the engine. The nozzle (10) comprises a port (12) having an internal annular surface (13) and a valve member (20) having an external annular surface coaxial with respect the internal annular surface. Sealing contact between the valve member and the port is provided therebetween along a circular seat line substantially coaxial to the respective annular surfaces. The annular surfaces are configured so that when the internal and external annular surfaces are in sealing contact along the circular seat line, the seat line is located adjacent the downstream end of the passage for delivery of fuel with respect to the direction of the flow of fuel through the passage. The maximum width of the passage between the annular surfaces is not substantially more than 30 microns.