  Any stellar system with a star formation history (SFH) more extended than a
massive star's lifetime will be composite in metallicity. Our method of
chemically consistent evolutionary synthesis tries to account for the
increasing initial metallicity of successive generations of stars. Using
various sets of input physics for a range of metallicities $10^{-4} \leq Z \leq
0.05$ we keep track of the ISM enrichment and follow successive generations of
stars using stellar evolutionary tracks, yields, model atmosphere spectra,
index calibrations, etc., appropriate for their respective initial
metallicities. Since the SFH determines the evolution not only of the
metallicity, but, in particular, of abundance ratios of specific elements,
stellar evolution and galaxy evolution become intimately coupled. I review the
concept of chemically consistent evolution, present results for the
photometric, spectral, and chemical evolution of galaxies of various types in
the local Universe and at high redshift, and discuss its advantages as well as
its current limitations.
