Mid-infrared electroluminescence with colloidal quantum dots is explored. With the interband transition, 4 µm electroluminescence is demonstrated using a pn junction and HgTe dots. The external quantum efficiency reaches ~10-3 and the power conversion efficiency reaches ~10-4 under biases of a few volts. The efficiency is limited by the photoluminescence of the quantum dots. Intraband electroluminescence at 5 µm is studied with partially n-doped HgSe/CdSe and HgSe/CdS dots. The unipolar device enables vertical or planar structures without additional charge transport layers. The device works at a large bias of 20-30 V. The external quantum efficiency is much higher than the photoluminescence quantum yield, indicating a cascade mechanism, where each injected electron emits multiple photons. With an optical enhancement substrate, the external quantum efficiency reaches 15%, and the power conversion efficiency reaches 0.085%. The doping requirement is tested by modifying the surface condition of the dots and adding a bottom gate electrode. At room temperature, the intraband electroluminescence shows weak dependence on doping. Intraband electroluminescence at 6 µm is demonstrated with weakly n-doped HgTe dots and a planar structure. The intraband emission is further studied with intrinsic wide bandgap CdSe dots. With an electron injection layer and designed electrodes, intraband electroluminescence is observed at 5 µm. The intraband cascade electroluminescence opens new possibilities for mid-infrared light emitting devices. It is feasible with wide bandgap materials, and it could realize photoluminescence quantum yield limited efficiency with simple structures. Future directions, including improving photoluminescence and electrically driven intraband lasing, are discussed.