Large earth-based telescopes and the 'Hubble Space Telescope' are capable to measure spectral differences between different distant galaxies.It is clear that the spectrum of such a galaxy is the sum of the spectra of the stars in the galaxy. Individual stars can however not be observed.In order to interpret the observed spectrum of a distant galaxy one has to know exactly its contents: i.e. the fraction of stars with any possible spectral classification: i.e. evolutionary status. Every star is the result of either single star evolution either close binary star evolution. A complete library of single star evolution has been constructed by the research group at Geneva. Our group has nowadays the expertise to construct a complete library of star populations which are the outcome of close binary evolution.