Despite their potential for a range of exciting new applications, mobile eye trackers suffer from several fundamental usability problems. InvisibleEye is an innovative approach for mobile eye tracking that uses millimeter-size RGB cameras, which can be fully embedded into normal glasses frames, as well as appearancebased gaze estimation to directly estimate gaze from the eye images. Through evaluation on three large-scale, increasingly realistic datasets, we show that InvisibleEye can achieve a person-specific gaze estimation accuracy of up to 2.04° using three camera pairs with a resolution of only 3x3 pixels.