  I briefly review the method of population synthesis of binary stars and
discuss the preliminary results of a study of the Galactic population of
subdwarf B stars. In particular I focus on the formation of (apparently) single
sdB stars and their relation to (apparently) single helium-core white dwarfs. I
discuss the merits of mergers of two helium white dwarfs and interactions with
sub-stellar companions for explaining these single objects. A preliminary
conclusion is that the current observations suggest both mechanisms may
contribute, but that the helium white dwarfs are likely formed in majority from
interactions with sub-stellar companions.
