  The stellar populations of galaxies contain a wealth of detailed information.
  From the youngest, most massive stars, to almost invisible remnants, the
history of star formation is encoded in the stars that make up a galaxy.
Extracting some, or all, of this informationhas long been a goal of stellar
population studies. This was achieved in the last couple of decades and it is
now a routine task, which forms a crucial ingredient in much of observational
galaxy evolution, from our Galaxy out to the most distant systems found. In
many of these domains we are now limited not by sample size, but by systematic
uncertainties and this will increasingly be the case in the future.
  The aim of this review is to outline the challenges faced by stellar
population studies in the coming decade within the context of upcoming
observational facilities. I will highlight the need to better understand the
near-IR spectral range and outline the difficulties presented by less well
understood phases of stellar evolution such as thermally pulsing AGB stars,
horizontal branch stars and the very first stars. The influence of rotation and
binarity on stellar population modeling is also briefly discussed.
