Abstract: Significant advances in the room-temperature (RT) continuous-wave (CW) output power of both type-l quantum-well (QW) active-layer lasers and interband cascade lasers have been reported within the 3-4-¿m wavelength region in 2009. Recent developments on the growth of highly strained QWs and low-defect-density lattice-mismatched materials also demonstrate potential for realizing high-performance mid-infrared (IR) lasers on conventional substrates such as Si, GaAs, and inP.