In recent years a new generation of model atmosphere codes, which include the effects of metal line blanketing of millions of spectral lines in NLTE, has been used to re-determine the properties of massive stars through quantitative spectral analysis methods applied to optical, IR and UV spectra. This has resulted in a significant change of the effective temperature scale of early-type stars and a revision of mass-loss rates. Observed mass-loss rates and effective temperatures depend strongly on metallicity, both in agreement with theoretical predictions. The new model atmospheres, in conjunction with the new generation of 10-m-class telescopes equipped with efficient multi-object spectrographs, have made it possible to study blue supergiants in galaxies far beyond the Local Group in spectroscopic detail to determine accurate chemical composition, extinction and distances. A new distance determination method, the flux-weighted gravity–luminosity relationship, is discussed as a very promising complement to existing stellar distance indicators.

Observationally, there are still fundamental uncertainties in the determination of stellar mass-loss rates, which are caused by evidence that the winds are inhomogeneous and clumped. This may lead to major revisions of the observed rates of mass loss.