This text is a lucid presentation of the principles of working of all types of sensors and transducers which form the prime components of the instrumentation systems. The characteristics of the sensors and transducers and the operating principles of transducer technologies have been discussed in considerable detail. Besides covering conventional sensors such as electro-mechanical, thermal, magnetic, radiation, and electro-analytical, the recent advances in sensor technologies including smart and intelligent sensors used in automated systems are also comprehensively described. The application aspects of sensors used in several fields such as automobiles, manu- facturing, medical, and environment are fully illustrated. With a straightforward approach the text is aimed at building a sound understanding of the fundamentals, and inculcating analytical skills needed for design and operation. Numerous schematic representations, examples, and review questions help transcend underlying basics to automation and instrumentation. The book with incisive explanations and all the pedagogic attributes is designed to serve the needs of the engineering students of instrumentation, chemical, mechanical, and electrical disciplines. It will also be a useful text for the students of applied sciences.