High-power fiber lasers have experienced dramatic development over the past few decades. Further upscaling of the laser power greatly depends on the development of laser fibers with an enlarged large-mode area (LMA) while maintaining a single-mode (SM) output, which can effectively reduce the power density and mitigate the influence of nonlinear and thermo-optic effects that induce transverse mode instability (TMI). The development of fiber lasers is inseparable from the advancement of laser fibers from conventional step-index fibers to maturing large mode area (LMA) double-clad fibers and microstructured fibers (MOFs). This chapter begins with a brief history and overview of LMA fibers and then summarizes the most recent research progress on the structural design principles and fabrication of solid-core LMA fibers, which are made mainly of silica-based glasses, as well as their applications in high-power fiber lasers.