The Life and Times of Giant Molecular Clouds
  Giant molecular clouds (GMCs) are the sites of star formation and stellar
feedback in galaxies. Their properties set the initial conditions for star
formation and their lifecycles determine how feedback regulates galaxy
evolution. In recent years, the advent of high-resolution telescopes has
enabled systematic GMC-scale studies of the molecular interstellar medium in
nearby galaxies, now covering a wide range of physical conditions and allowing
for the first studies of how GMC properties depend on galactic environment.
These observational developments have been accompanied by numerical simulations
of improving resolution that are increasingly accurately accounting for the
effects of the galactic-scale environment on GMCs, while simultaneously
improving the treatment of the small-scale processes of star-formation and
stellar feedback within them. The combination of these recent developments has
greatly improved our understanding of the formation, evolution, and destruction
of GMCs. We review the current state of the field, highlight current open
questions, and discuss promising avenues for future studies.
