  We present a combined analysis of the low-mass Initial Mass Function (IMF)
for seven star forming regions. We first demonstrate that the ratios of stars
to brown dwarfs are consistent with a single underlying IMF. Assuming the
underlying IMF is the same for all seven clusters and by combining the ratio of
stars to brown dwarfs from each cluster we constrain the shape of the brown
dwarf IMF and find it to be consistent with a log--normal IMF. This provides
the strongest constraint yet that the sub-stellar IMF turns over (dN/dM
M^(-alpha), alpha < 0).
