  Wolf-Rayet stars (WRs) represent the end of a massive star's life as it is
about to turn into a supernova. Obtaining complete samples of such stars across
a large range of metallicities poses observational challenges, but presents us
with an exacting way to test current stellar evolutionary theories. A technique
we have developed and refined involves interference filter imaging combined
with image subtraction and crowded-field photometry. This helps us address one
of the most controversial topics in current massive star research: the relative
importance of binarity in the evolution of massive stars and formation of WRs.
Here we discuss the current state of the field, including how the observed WR
populations match with the predictions of both single and binary star
evolutionary models. We end with what we believe are the most important next
steps in WR research.
