  The method of spectral disentangling has now created the opportunity for
studying the chemical composition in previously inaccessible components of
binary and multiple stars. This in turn makes it possible to trace their
chemical evolution, a vital aspect in understanding the evolution of stellar
systems. We review different ways to reconstruct individual spectra from
eclipsing and non-eclipsing systems, and then concentrate on some recent
applications to detached binaries with high-mass and intermediate-mass stars,
and Algol-type mass-transfer systems.
