Cool Stars 14 - Submitted Abstract # 165 This version created on 05 October 2006 Uncertainties in Brown Dwarf Models Travis Barman, Lowell Observatory Brown dwarf discoveries now span a considerable range in temperature, mass, and age down to newly formed (or still forming!) objects, planetary masses, and extremely cool atmospheres. These observational discoveries have revealed many successes and failures of our current state-of-the-art theoretical models. Models in the form of synthetic spectra, isochrones, and mass-luminosity diagrams provide conveniently packaged descriptions for "the theory" of brown dwarfs. However, buried inside are many assumptions, approximations, and a variety of arbitrary choices. Nevertheless, these models are very powerful tools for inferring the basic properties of brown dwarfs despite their limitations. This talk will summarize the current state of spectroscopic models and the challenges they face with an emphasis on the L/T spectral type transition, low-gravity dwarfs, and modeling low metallicity sub-dwarfs. ----------------------------------