  The essential features of the stellar Initial Mass Function are, rather
generally, (1) a peak at a mass of a few tenths of a solar mass, and (2) a
power-law tail toward higher masses that is similar to the original Salpeter
function. Recent work suggests that the IMF peak reflects a preferred scale of
fragmentation associated with the transition from a cooling phase of collapse
at low densities to a nearly isothermal phase at higher densities, where the
gas becomes thermally coupled to the dust. The Salpeter power law is plausibly
produced, at least in part, by scale-free accretion processes that build up
massive stars in dense environments. The young stars at the Galactic Center
appear to have unusually high masses, possibly because of a high minimum mass
resulting from the high opacity of the dense star-forming gas.
