Massive star clusters are invaluable bridges connecting the interstellar medium, star formation and evolution, the evolution of galaxies, and cosmology. These very complex systems are studied in every wavelength region, from radio to gamma rays, and they are also relevant for gravitational wave detectors. A complete understanding of these systems and of their stellar populations is a challenging task. It requires the exchange of ideas and the collaboration of astrophysicists with observational, theoretical, and numerical expertise in stellar evolution, interstellar matter magnetohydrodynamics, stellar dynamics, the formation and evolution of galaxies, cosmology, multidimensional numerical simulations, N-body simulations, and multi-wavelength high-precision photometry, spectroscopy, and astrometry. IAU Symposium 316 addresses all these varied aspects, with observers, theoreticians, and modellers discussing controversial topics and planning the next steps in the key open areas. This volume is particularly timely as we enter a golden age for observations and numerical multidimensional simulations.