This book gives an overview of the present trends in a rapidly growing interdisciplinary field, namely the research and development of biosensors. It focuses on the development of new biosensors which combine the sensitivity and specificity of biological systems (enzymes, immunosystems, microbial cells, tissue, plants, etc.) with the efficiency of electrochemical transducers. The molecular mechanisms of the processes in biosensors as well as the new methods for transduction and immobilization of biosystems are described in detail. Also, important fields of application are evaluated, i.e. medicinal chemistry including in vivo monitoring, environment pollution monitoring, biotechnology process control, determination of food contaminants and food quality control.