This book is aimed at scientists, technologists, engineers, and undergraduate and graduate students involved in analytical and process biochemistry and biotechnology. It reviews the potentialities of light-emitting reaction associated with the sensor approach.The book introduces the concepts of sensors and biosensors and places bio- and chemi-luminescent sensors in the general context of biosensors. It then briefly describes luminescence phenomena and provides some basic knowledge necessary for understanding and exploiting light-emitting reactions. These luminescence reactions, important from an analytical standpoint, are described. Also the applications of bio- and chemi-luminescence which make use of immobilized reagents are explained. Finally, there is discussion of bio- and chemi-luminescent sensors, most of them including fiber optics.