  I present new results from a continuing program to identify and characterize
the low-mass stellar and substellar populations in the young cluster IC 348
(1-10~Myr). Optical spectroscopy has revealed young objects with spectral types
as late as M8.25. The intrinsic J-H and H-K colors of these sources are
dwarf-like, whereas the R-I and I-J colors appear intermediate between the
colors of dwarfs and giants. Furthermore, the spectra from 6500 to 9500 A are
reproduced well with averages of standard dwarf and giant spectra, suggesting
that such averages should be used in the classification of young late-type
sources. An H-R diagram is constructed for the low-mass population in IC 348
(K6-M8). The presumably coeval components of the young quadruple system GG~Tau
(White et al.) and the locus of stars in IC 348 are used as empirical
isochrones to test the theoretical evolutionary models. For the models of
Baraffe et al., an adjustment of the temperature scale to progressively warmer
temperatures at later M types, intermediate between dwarfs and giants, brings
all components of GG~Tau onto the same model isochrone and gives the population
of IC 348 a constant age and age spread as a function of mass. When other
observational constraints are considered, such as the dynamical masses of
GM~Aur, DM~Tau, and GG~Tau~A, the models of Baraffe et al. are the most
consistent with observations of young systems. With compatible temperature
scales, the models of both D'Antona & Mazzitelli and Baraffe et al. suggest
that the hydrogen burning mass limit occurs near M6 at ages of <10 Myr. Thus,
several likely brown dwarfs are discovered in this study of IC 348, with masses
down to ~20-30 M_J.
