The advent of the world’s first hard x-ray free-electron laser (FEL) – the Linac Coherent Light Source free-electron laser at SLAC – in one step in 2009 increased the spectral brightness of x-ray sources on Earth by a factor of a billion. Spatially coherent, monochromatic, femtosecond X-ray pulses can now be routinely produced over a wide spectral range, enabling simultaneous access to the spatial and temporal scales of atomic processes for the first time. These advances are enabling fascinating new developments in fields as diverse as x-ray diffraction imaging of biological systems, nonlinear x-ray optics and the investigation of matter in extreme conditions of temperature and density relevant to astrophysical and inertial confinement fusion. In this talk I'll give an overview of some of the most important work done to date on x-ray FELs, and speculate on future research directions and opportunities.