The Third Edition of this best-selling textbook continues the successful approach adopted by previous editions - It is an introduction to optoelectronics for all students, undergraduate or postgraduate, and practicing engineers requiring a treatment that is not too advanced but gives a good introduction to the quantitative aspects of the subject. The book aims to put special emphasis on the fundamental principles which underlie the operation of devices and systems. Readers will then be able to appreciate the operation of devices not covered in the book and to understand future developments within the subject. All the material in this edition has been fully updated.