The lasers wherein the active gain medium is an optical fiber doped with rare-earth elements, such as erbium, neodymium, praseodymium, thulium and holmium, are termed as fiber lasers. The laser light in fiber lasers is both generated and delivered by an inherently flexible medium that allows easier delivery to the focusing location and target. These lasers have active regions several kilometres long in order to provide high optical gain. They exhibit high temperature and vibrational stability and extended lifetime. They play an important part in laser cutting, folding of metals and welding. Most of the topics introduced in this book cover new technology and the applications in this discipline. It brings forth some of the most innovative concepts and elucidates the unexplored aspects of fiber lasers. For all those who are interested in fiber lasers, this book can prove to be an essential guide.