In this paper we discuss physics and applications of light emission in SiGe nanostructures. In order to be commercially valuable, these light emitters should be efficient, fast, and operational at room temperature. Another important requirement is in the emission wavelength, which should match the optical waveguide low-loss spectral region, i.e., 1.3-1.6 μm. Among other approaches, epitaxially-grown Si/SiGe quantum wells and quantum dot/quantum well complexes produce efficient photoluminescence and electroluminescence in the required spectral range. Until recently, the major roadblocks for practical applications of these devices were strong thermal quenching of the luminescence quantum efficiency and a long carrier radiative lifetime. The latest progress in the understanding of physics of carrier recombination in Si/SiGe nanostructures is reviewed, and a new route toward CMOS compatible light emitters for on-chip optical interconnects is proposed.