Carbohydrates are involved in crucial physiological and pathological events. One can take advantage of carbohydrate-based interaction for drug discovery, diagnosis, antibiotics, vaccine, etc. This chapter deals with biosensors and microarrays that take advantage of carbohydrates-based interactions with a special interest in devices that are designed for medical applications. A large overview of glycochemistry, followed by the biological role of carbohydrates, is given. Carbohydrate-based biosensors are then described with special emphasis on surface chemistry and signal transduction. Finally, medically relevant applications illustrate the use of carbohydrates as recognition receptors in biosensing.