A fuel injector for an internal combustion engine, the fuel injector comprising an injector body, a fuel supply passage defined in the injector body, the fuel supply passage containing fuel under high pressure in use of the injector, a pressure sensor for measuring the pressure of fuel in the passage in use, wherein the pressure sensor is situated within the injector body and is separated from fuel in the passage in use, and a method of fuel injection, comprising constructing an hydraulic behavior profile by fuel pressure measurement, using the hydraulic behavior profile to predict fuel pressure that will prevail in a fuel injector during an injection event, and supplying a control signal to the fuel injector to control the amount of fuel injected during the injection event in accordance with the predicted fuel pressure. By predicting the fuel pressure that will prevail during an injection event, the fuel delivered during the injection event can be accurately controlled.