The development of high-power continuouswave (CW) single-mode fibre lasers operating at wavelengths of 1 μm has been ongoing for most of the past decade, and great progress has indeed been made in scaling the output power of such devices. Notable milestones include the demonstration of 100 W of CW power in 1999, followed by 1 kW in 2004 and more recently the demonstration of a 10 kW single-mode fibre device by IPG Photonics. One of the early factors that enabled such successful power scaling was the adoption of large-mode-area (LMA) fibres as an alternative to conventional high numerical aperture (NA), small mode-field diameter fibre designs inherited from the telecommunications industry. Increasing the size of the mode field by using fibres with larger cores and lower NA made it possible to overcome the nonlinear limitations associated with high intensities in conventional fibres.