  In this review I first summarize why binaries are key objects in the study of
stellar populations, key objects to understand the evolution of star clusters,
key objects to understand galaxies and thus the universe. I then focus on 4
specific topics:
  1. the formation (via binaries) and evolution of very massive stars in dense
clusters and the importance of stellar wind mass loss. I discuss preliminary
computations of wind mass loss rates of very massive stars performed with the
Munich hydrodynamical code, and the influence of these new rates on the
possible formation of an intermediate mass black hole in the cluster MGG 11 in
M82
  2. the evolution of intermediate mass binaries in a starburst with special
emphasis on the variation of the SN Ia rate (the delayed time distribution of
SN Ia). A comparison with SN ia rates in elliptical galaxies may provide
important clues on the SN Ia model as well as on the evolution of the SN Ia
progenitors
  3. the evolution of the double neutron stars mergers in a starburst (the
delayed time distribution of these mergers) and what this tells us about the
suggestion that these mergers may be important production sites of r-process
elements
  4. the possible effect of massive binaries on the self-enrichment of globular
clusters.
