Abstract: The types, principles, status and applications of biosensors are reviewed. Biosensors are a new kind of sensor that uses biological molecules as the sensoring element. Chemical, thermal and optical signals can be converted into electrical signals, or an electrical signal can be directly produced and amplified. Biosensors are widely used in food production, environmental inspection, fermentation industry, defence and clinical medicine. They are mainly used for determining the concentration of food and contamination, the respiration activity and selection of cultivation methods for microorganisms, as well as the final process in water treatment. It can be expected that future developments will aim at miniaturization, practicality, diversification and artifical intelligence. They may also be used for research on artifical sense organs. Swift, accurate and convenient to use, biosensors have broad application prospects, and a new place in the market.