  Blue Supergiants (BSGs) are the brightest stars in the universe at visual
light with absolute magnitudes up to Mv=-10 mag. They are ideal stellar objects
for the determination of extragalactic distances, in particular, because the
perennial uncertainties troubling most of the other stellar distance
indicators, interstellar extinction and metallicity, do not affect them. The
quantitative spectral analysis of low resolution spectra of individual BSGs
provides accurate stellar parameters and chemical composition, which are then
used to determine accurate reddening and extinction from photometry for each
individual object. Accurate distances can be determined from stellar gravities
and effective temperatures using the "Flux Weighted Gravity - Luminosity
Relationship (FGLR)". Most recent results of the quantitative spectral analysis
of BSGs in galaxies within and beyond the Local Group based on medium and low
resolution spectra obtained with the ESO VLT and the Keck telescopes on Mauna
Kea are presented and distances obtained with the FGLR-method are discussed
together with the effects of patchy extinction and abundance gradients in
galaxies. BSG metallicities and metallicity gradients are compared with results
from strong-line HII region studies and the consequences for the empirical
calibration of the metallicity dependence of the Cepheid period-luminosity
relationship are pointed out. The perspectives of future work are discussed,
the use of the giant ground-based telescopes of the next generation such as the
TMT on Mauna Kea and the E-ELT and the tremendous value of the GAIA mission to
allow for the ultimate calibration of the FGLR using galactic BSGs.

Cosmology and Nongalactic Astrophysics;Solar and Stellar Astrophysics