Biosensors combine the recognition power of biological systems with advanced transducers and microelectronics to yield analytical instruments with unique measurement capabilities. The new generation of electrochemical blood-glucose monitors are widely used by diabetic people in their homes. While the measurement of glucose currently dominates commercial activity in the biosensor field, simple inexpensive instruments can be constructed to measure thousands of other analytes. These instruments have applications in medicine, the pharmaceutical industry, the environment, the food and process industries, as well as in security and defense.