A biosensor is a device for the detection of an analyte that combines a biological component with a physiochemical detector component. A typical biosensor consists of three parts: a sensitive biological element, a transducer in between and a detector element. The most widespread example of a commercial biosensor is the blood glucose biosensor, which uses an enzyme to break blood glucose down. In so doing it transfers an electron to an electrode and this is converted into a measure of blood glucose concentration. The high market demand for such sensors has fuelled development of associated sensor technologies. This book covers recent developments that combine the fields of biotechnology and electrical engineering with applications in the detection of very low levels of chemicals and biological agents in the body. It provides an authentic overview of a wide range of biosensing systems, discussing the elements of different transducers used in sensors and the selective elements that are employed. The style is relatively non-mathematical and informal in approach. The contents of the book will be ideal for graduate and postgraduate students of biotechnology, analytical and physical chemistry. It will also be invaluable to all those concerned with the environmental and biomedical applications of such biosensing systems.