In this paper, we review the current theory of very low mass stars model atmospheres including the coolest known M~dwarfs, M~subdwarfs, and brown dwarfs, i.e. T$_{ eff} \leq 5,000 $K and $-2.0 \le [M/H] \le +0.0$. We discuss ongoing efforts to incorporate molecular and grain opacities in cool stellar spectra, as well as the latest progress in deriving the effective temperature scale of M~dwarfs. We also present the latest results of the models related to the search for brown dwarfs.
Categories: astro-ph