The Space Telescope Science Institute Symposium on Massive Stars: From Pop III and GRBs to the Milky Way took place during May 8–11, 2006.

These proceedings represent only a part of the invited talks that were presented at the symposium. We thank the contributing authors for preparing their manuscripts.

Traditionally, massive stars played the important roles of being responsible for supernova explosions, of being the progenitors of stellar-mass black holes, and of producing heavy elements. In recent years, massive stars have gained additional importance in our understanding of cosmic history. Very massive stars (Population III) are now recognized as constituting the first population of stars in the universe, and massive stars have been identified as being the progenitors of the long-duration Gamma-ray Bursters. In addition, very massive stars may produce supernova explosions by a new mechanism—pair instability—that has been anticipated theoretically, but has never been unambiguously detected (the recent SN 2006gy may have been such an event).

The ST ScI symposium on Massive Stars attempted to capture all the aspects involved in the astrophysics of massive stars.

We thank Sharon Toolan of ST ScI for her help in preparing this volume for publication.