  The characteristic mass M_c and slope Gamma of the IMF are reviewed for
clusters, field regions, galaxies, and regions formed during cosmological
times. Local star formation has a somewhat uniform M_c and Gamma. Statistical
variations in Gamma are summarized, as are the limitations imposed by these
variations. Cosmological star formation appears to have both a higher M_c and a
slightly shallower slope at intermediate to high stellar mass. The center of
the Milky Way may have a shallow slope too. Field regions have slightly steeper
slopes than clusters, but this could be the result of enhanced drift of low
mass stars out of clusters and associations. Dwarf galaxies also have steeper
slopes. Results from the observation of pre-stellar clumps are reviewed too.
Pre-stellar clumps appear to have about the same mass function as stars and are
therefore thought to be the main precursors to stars. If this is the case, then
the IMF is generally determined by gas-phase processes. Brown dwarf formation
also shares many characteristics of star formation, suggesting that they form
by similar mechanisms.
