CO2 and YAG lasers are routinely capable of producing cw output powers in the range of sub-W to multi-kW and as such have become the mainstay of the laser cutting and welding industry. Despite numerous advancements in their design, these lasers are still typified by poor wallplug efficiencies (typically 1-10%) and/or relatively poor optical beam qualities. On the other hand, recent developments in laser diode technology, fiber design and beam combining techniques have meant that cladding pumped ytterbium-doped fiber lasers have attracted growing interest as a route to highly efficient (20-40% wallplug efficiencies), high output power, high beam quality (near-diffraction limited) lasers for a vast array of material processing applications. More specifically fiber lasers have a number of distinct advantages over their more conventional alternatives including size, reliability, wavelength selectivity, heat dissipation, wallplug efficiency, and operational cost. Furthermore, they can be operated without the need for active cooling or optical alignment. In this paper we review the recent progress in fiber design that is facilitating the scalability of the output power of fiber-based lasers and amplifiers.