Elastic Optical Networks (EON) is widely accepted today as the next step in the evolution toward high capacity networking. The idea behind it is to optimize the use of resources by flexibly assigning spectrum, data rate and modulation format adapted to the needs of the end-to-end connection requests. This book is devoted to the study of three important issues in EONs, 1) dynamic source aggregation of sub-wavelength connections, 2) correlation between traffic granularity and defragmentation periodicity and 3) using spectrum fragmentation to better allocate time-varying connections.