Since the development of the glucose sensor by Clark and Lyons in 1962, generally recognized as the first biosensor, many types of sensor have been developed in which a physical or chemical transducer is provided with a layer containing a biological sensing elements. The resulting device is called a biosensor, aimed to produce an electronic signal as a function of the condensation of a chemical or biochemical constituent of a liquid, not necessarily of biological origin. Among the many proposed concepts, the integration of biologically active materials with a silicon chip is one of the most intriguing approaches, because it seems the most comprehensive integration between biology and electronics. In this chapter, we focused on Biosensors their applications and development and research in biosensors based on principles, will be described and discussed with an outlook on the future.