Published online by Cambridge University Press: 26 May 2016
Massive stars provide most of our current knowledge of the first star forming galaxies in the universe via their ultraviolet and optical spectra redshifted into the visible and near-infrared bands. Here I briefly review the growing body of data on these early stellar populations from which star formation rates, the initial mass function, chemical abundances, ages, and dust reddenings are being deduced. New evidence also shows the dramatic impact which massive stars have on their galactic and intergalactic environments.