This volume is the fourth in a series of annual reviews on progress in the research and technology, both basic and applied, of chemical sensors. New principles, new devices, and the detailed mechanism of various chemical sensors are described. Chemical sensors continue to grow rapidly in importance encompassing a broad spectrum of technologies covering safety, pollution, fuel economy, medical engineering and industrial processes. More than half the papers in this volume are relevant to biosensing, a strategic field for medical and health care equipment, especially in geriatric medicine. Frequent health checks at home will be increasingly necessary as the proportion of the aged in the population steadily grows. In some cases health conditions will have to be monitored constantly to give warnings or provide emergency assistance at the right time. Because biochemical substances play major roles in physiological processes such as metabolism, excitation and contraction of skeletal muscle and neurotransmission, chemical sensing of the related biochemical substances will eventually become indispensable.Each chapter is written by an expert active in the front lines of chemical sensor research. Not only is the technological essence of the subject provided, but also the background and philosophy, an evaluation of achievements to date and problems to be dealt with. Each topic is described in sufficient depth to be useful to researchers worldwide.