Is there a fundamental mass scale to the star-formation process between the limiting mass required to ignite hydrogen and deuterium burning in the interiors of young stellar objects? How much baryonic mass is locked up in sub-stellar objects in the disk of the Milky Way? Advances in the instrumentation and techniques of near-infrared spectroscopy have enabled us to begin addressing these questions directly. Within the past several years, bona fide brown dwarfs and extrasolar planets have been found in open clusters as well as in the solar neighborhood. However, the frequency of such objects in our Galaxy (and other galaxies) remains unknown. Regions of recent star formation have been fertile ground for the discovery of very young brown dwarfs because substellar objects are much more luminous in their youth and the parent molecular cloud provides an effective screen against background field stars. Does the shape of the IMF depend critically on the initial conditions from which the stars form? Studies of the stellar mass functions of young clusters from 0.1-10.0 Msun have shown that they do not vary wildly from region to region and are broadly consistent with having been drawn from the field star IMF (Meyer et al. 2000, PPIV). Recent studies utilizing the current generation of 6-10m telescopes as well as the unique capabilities of NICMOS on HST have begun to constrain the sub-stellar IMF. By combining high resolution NICMOS observations of the central regions of embedded clusters with optical/IR spectroscopy of cluster members, we can constrain the ratio of stellar-to-sub-stellar objects in nearby star-forming regions. Comparing these results to other studies of the sub-stellar IMF suggest that the universality characterizing the emergent mass distributions of young clusters extends below the hydrogen burning limit. Pushing such studies to distant regions of more extreme star formation will be discussed.