A force sensor particularly suited for use in an electronic stylus that senses the contact force on its nib for recording pen strokes and handwriting recognition. The sensor has a load bearing member movably mounted for receiving an input force to be sensed, the load bearing member being biased against the direction of the input force. The sensor also has a light source, a photo-detector for sensing levels of illumination from the light source and circuitry for converting a range of illumination levels sensed by the photo-detector into a range of output signals. During use, the illumination level sensed by the photo-detector varies with movement of the load bearing member such that the output signal from the circuitry is indicative of the input force. Using an optical sensor avoids the need to use a delicate piezo-resistive sensor that requires careful tolerancing during production.