  Techniques to extract information from spectra of unresolved multi-component
systems are revised, with emphasis on recent developments and practical
aspects. We review the cross-correlation techniques developed to deal with such
spectra, discuss the determination of the broadening function and compare
techniques to reconstruct component spectra. The recent results obtained by
separating or disentangling the component spectra is summarized. An evaluation
is made of possible indeterminacies and random and systematic errors in the
component spectra.
