Nowadays, thanks to the utilization of Raman fiber amplifiers, of new fibers, of new techniques for broadband dispersion compensation and broadband dispersion management, the potential bit-rate per WDM channel has increased to 40Gb/s and higher. Unfortunately, the capability of switching and routing will never been able to support the perspective spectacular improvement on transmission capability if it will be still implemented using only the convectional hard-wired architecture. Short-haul optical interconnection is the most promising candidate for providing a solution for hard-wired deadlock. Therefore, this book deals with the topic of optical interconnections with aim of seeking new architectures an subsystems to be adopted at multiple hierarchic levels of a WDM network: in part I we focus on long-haul or local-area optical scenarios characterized by kilometric distances between devices; in part II we study the innovative optical interconnection scenarios on uncommon optical distances “inside the box" (in the order of meters/centimetres), i.e., to implement rack-to-rack and backplane connections.