Despite the importance of sprays to engine combustion, understanding has been hampered by the sensitivity of spray behavior to unknown nozzle geometry effects. The Engine Combustion Network (ECN) collaboration has focused on overcoming this impediment to spray research by focusing on a set of nominally identical diesel injectors. Detailed measurements of the nozzle geometry for the four ECN Spray A injectors (90 mu m diameter, axial single-hole nozzles) have been performed using x-ray tomography, x-ray phase-contrast imaging, silicone molding, and optical microscopy. Measurements of the needle motions (axial and lateral) and hydraulic performance of the nozzles have also been performed. Measurements of the nozzle geometry show that all of the nozzle holes are offset from the axis of the needle and sac. This offset creates an asymmetry in the inlet condition of the nozzle hole, which varies from nozzle to nozzle. The nozzle profile deviates significantly from the nominal specification, with an abrupt convergence of the nozzle holes near the nozzle exit seen in all of the injectors. Nozzle diameter measurements show a smaller diameter than the nominal specification, with significant differences between the injectors. Needle lift measurements show oscillatory behavior in both the axial and lateral motions of the needle. The hydraulic characterization of the nozzles demonstrates the impact of internal geometry (outlet diameter) on momentum and mass flow rate.