This book analyzes novel possibilities offered to the telecommunication engineer in designing tomorrow's optical networks. Currently, optical and optoelectronic technologies make possible the realization of high-performance optical fiber communication systems and networks with the adoption of WDM configurations and both linear and nonlinear optical amplifications. The last step for increasing network throughput is represented by the implementation of multidimensional modulation formats in coherent optical communication systems, which enable increasing the bit rate/channel toward 400 Gbit/s/channel and beyond. Following this approach, the main emphasis is placed on innovative optical modulations. Multidimensional Modulations in Optical Communication Systems is an essential guide to the world of innovative optical communications from the point of view of growing capacity and security. It guides researchers and industries with the aim to exploring future applications for optical communications.