Modern communication technologies have revolutionized society and econ­ omy on a global scale, and progress in this field is still breathtaking. Among the crucial features of these developments is the possibility to transmit/receive ever-increasing bit rates at lower and lower cost. This is due to some ex­ tent to improved electronics, but it is much more due to the capabilities of opticaL fibre-based communication systems. Optical communication tech­ nologies were initially introduced in order to improve traditional information exchange, but they have recently become a key prerequisite for the tremen­ dous growth in internet traffic, and optical technologies will be even more important in enabling and supporting the future expansion of internet traffic with annual growth rates forecast at 100%-200%. It is the purpose of the present book to describe the enabling components of optical communication systems, in particular their fundamentals, principles and current status, as well as the potential for future developments. Following such a scheme, it is the editors' hope that this book will not only attract the attention of experts already working in the field, but be, at least, likewise directed to interested newcomers. The book is organized into eleven chapters addressing the essential optical and optoelectronic components which form the hardware basis of today's, and most likely of future, optical networks.