Knowledge about the chemical abundances of objects of various ages in the Magellanic Clouds is essential for our understanding of their evolution in the past. The abundances of their lighter elements have been derived from spectra of HII regions, and those of the heavier elements from spectra of supergiants. An extensive study was carried out by Pagel et al. (1978). A summary of the composition of the HII regions was presented by Dufour (1984). Little has changed since then. The summary is still often used as a reference for comparison with stellar abundances, and it is therefore reproduced in Table 11.1.

A problem in interpreting the many results derived for the metallicity of cluster and field stars is the model dependence. The early works pointed towards an underabundance in the cluster stars relative to the field stars, but, as will be seen below, there is a clear tendency towards more and more agreement in metallicity between cluster and field stars. Differences have also frequently been found between the chemical abundances of the ISM and the stars in the Clouds, though warnings against overinterpreting the observational results have been given (Pagel 1993). The uncertainties in the derived data, for the stars as well as for the ISM, are still considerable.

For the study of the stellar abundances in the Magellanic Clouds only the most luminous and most extreme supergiants (A-type, Mv ≤ −9) were available for high-dispersion studies up to about 1975.