The Complex Upper HR Diagram
  Several decades of observations of the most massive and most luminous stars
have revealed a complex upper HR Diagram, shaped by mass loss, and inhabited by
a variety of evolved stars exhibiting the consequences of their mass loss
histories. This review presents a brief historical overview of the HR Diagram
for massive stars, highlighting some of the primary discoveries and results
from their observation in nearby galaxies. The chapters in this volume include
reviews of our current understanding of different groups of evolved massive
stars, all losing mass and in different stages of their evolution; the Luminous
Blue Variables (LBVs), B[e] supergiants, the warm hypergiants, Wolf-Rayet
stars, and the population of OB stars and supergiants in the Magellanic Clouds.
