Environments of massive stars and the upper mass limit
  The locations of massive stars (> 8 Msun) within their host galaxies is
reviewed. These range from distributed OB associations to dense star clusters
within giant HII regions. A comparison between massive stars and the
environments of core-collapse supernovae and long duration Gamma Ray Bursts is
made, both at low and high redshift. We also address the question of the upper
stellar mass limit, since very massive stars (VMS, Minit >> 100 Msun) may
produce exceptionally bright core-collapse supernovae or pair instability
supernovae.
