This book reflects the current knowledge and trends in the field of biosensors for environmental monitoring. Biosensors combine the power of microelectronics with the selectivity and sensitivity of biological components to detect individual substances or groups of substances in the environment. Biosensors can also be used for recognizing biological effects such as genotoxicity, immunotoxicity and endocrine responses. For this purpose, components of biological origin such as microorganisms, enzymes, receptors or specific nucleic acid sequences are applied for the recognition and combined with a transducer system to provide toxicologic or pharmacologic data within seconds. This approach is expected not only to provide a significant contribution to measurement technology but also a basis for competent political decisions.