This book elucidates the principles of free electron lasers with the help of valuable information. It talks about the basics and patterns of different free electron laser systems, ranging from infrared to XUV wavelength regimes. Besides discussing and comparing with traditional lasers, matters like near-field and cavity electrodynamics, compact and table-top arrangements and strong radiation induced exotic states of matter have also been assessed. The management and evaluation of such instruments and radiation safety problems have also been described. This book presents a set of research results on these sources of radiation, relating to primary principles, applications and some recent captivating ideas of current interest.