Biosensors, or sensors based on biological materials,are commonly used and essential tools to a wide variety of researchers working in a broad range of fields.This text presents a systematic and comprehensive introduction to the principles features of biosensors. Detailed performance characteristics of a broad range of biosensors are discussed. Details of the most important types of biosensors currently use are presented. Details of biosensor experiments for undergraduate and postgraduate students are included, while applications of biosensors across a range fields e.g.medicine, the food industry and environmental science, are considered in the closing chapter. The author provides a comprehensive introcduction to an increasingly important technique in a chemical analysis.