Fiber lasers combine highest beam quality and effi ciency, both in continuous and pulsed operation. These lasers have established themselves in industrial applications alongside gas and solid-state lasers and have partially replaced them since they can be designed monolithically and, therefore, very robustly without needing free-space components. Thanks to its high flexibility of output parameters, such as power, wavelength or pulse shape, fiber lasers can be used for a wide range of applications: in material processing, e. g. for ablation and welding, interferometry in metrology, or in medical technology.