Abstract A microscopic many-body theory describing the optical and electronic properties of semiconductors and semiconductor nanostructures is briefly reviewed. At the semiclassical level, the optical response is computed using Maxwell's equations together with the semiconductor Bloch equations which describe the dynamics of the diagonal and the off-diagonal terms of the reduced single-particle density matrix. These equations include the coupling between the semiconductor and the optical field as well as Coulomb many-body interactions among the optically excited carriers. Under quasi-equilibrium conditions, luminescence spectra can be obtained from absorption spectra on the basis of the Kubo–Martin–Schwinger relation for conditions usually limited to the regime of optical gain (lasers). More generally, light emission has to be computed at a fully quantum mechanical level leading to semiconductor luminescence equations.