Due to the increasing throughput of modern egg grading machines, which grade up to 120 000 eggs per hour, the visual inspection of eggs by humans ("candling"), becomes a critical bottleneck in the egg sorting chain. In order to assure a high and consistent egg quality, researchers investigated the use of modern sensor technologies to replace the candling operation. During the last decades, several types of sensors were developed, and it is believed that these sensors will replace human candling in the near future. A first class of sensors is based on mechanical techniques and allows investigation of the physical shell quality, such as the presence of cracks and shell strength. A second class is based upon spectroscopic principles and allows the operator to "see" through the egg shell in order to determine the internal quality of the eggs, such as albumen pH and viscosity and the presence of inclusions such as blood and meat spots. A third class of sensors aims at mimicking the human eye by means of a camera and a software platform ("computer vision"). Besides these types of sensors, some others based on ultrasonic, magnetic resonance and electronic nose principles are investigated and discussed. This paper gives an overview of these modern sensor technologies for egg grading.