  We summarize recent observational and theoretical progress aimed at
understanding the origin of the stellar initial mass function (IMF) with
specific focus on galactic star-forming regions. We synthesize data from
various efforts to determine the IMF in very young, partially-embedded stellar
clusters and find: i) no significant variations in the low-mass IMF have been
observed between different star-forming regions; and ii) the mass distributions
of young stars just emerging from molecular clouds are consistent with having
been drawn from the IMF derived from field stars in the solar neighborhood.
These results apply only to gross characterizations of the IMF (e.g. the ratio
of high to low mass stars); present observations do not rule out more subtle
regional differences. Further studies are required in order to assess whether
or not there is evidence for a universal turnover near the hydrogen--burning
limit. We also provide a general framework for discussing theories of the IMF,
and summarize recent work on several physical mechanisms which could play a
role in determining the form of the stellar initial mass function.
