Book excerpt: This comparative tutorial describes the reasons behind device failures and provides practical information on what can be done to minimize failure-prone designs and enhance device reliability. The text demonstrates how, with such advantages as smaller size, low-cost and simple operation, LEDs are well suited for a wide range of applications - especially in the field of optical fibre communication. This book should prove of interest to engineers and scientists in research, design, manufacturing and development of semiconductor lasers, LEDs and optical transmission systems.