  Blue supergiant stars of B and A spectral types are amongst the visually
brightest non-transient astronomical objects. Their intrinsic brightness makes
it possible to obtain high quality optical spectra of these objects in distant
galaxies, enabling the study not only of these stars in different environments,
but also to use them as tools to probe their host galaxies. Quantitative
analysis of their optical spectra provide tight constraints on their evolution
in a wide range of metallicities, as well as on the present-day chemical
composition, extinction laws and distances to their host galaxies. We review in
this contribution recent results in this field.
