With its recent breakthrough in terms of output power and laser efficiency, the erbium-doped 3 μm laser has become an object of intense scientific research. With the improvement of high-quality low phonon energy laser gain media, especially the development of ceramic gain media, the 3 μm laser performance can be further improved by optimizing the wavelength and spectral linewidth of pump sources, doping concentration of Er-doped laser gain media, and laser cavity parameters. Compared with semiconductor laser and nonlinear frequency conversion technologies, the laser-diode pumped Er-doped laser emitting 3 μm wavelength is very promising, especially in the pulsed laser operation for producing high peak power and large pulse energy.