Chapter 1 introduces the challenges of network evolution and demands on capacity through several stages of developments. These stages range from a few Mbps over distances of a few hundreds of meters to hundreds of Giga-bps and even Tera-bps over thousands of kilometers, by novel modulation and reception techniques combining non-coherent and coherent transmission with advanced digital signal processing. The chapters to follow can be classified into three sections: Section I —Basic Principles of Optical Direct and External Modulation; Section II—The Implementation of Modulators in Coherent and Noncoherent Optical Transmissions Systems; and Section III—An Overview of Fabrication Techniques of Integrated Guided-Wave Photonic Modulators, Basic Principles of Modulation Schemes and Transmission Medium, and Single Mode/Few Mode Fibers.