  The new spectroscopic classes, L and T, are defined by the role of dust
clouds in their atmospheres, the former by their presence and the latter by
their removal and near absence. Moreover, the M to L and L to T transitions are
intimately tied to the condensation and character of silicate and iron grains,
and the associated clouds play pivotal roles in the colors and spectra of such
brown dwarfs. Spanning the effective temperature range from $\sim$2200 K to
$\sim$600 K, these objects are being found in abundance and are a new arena in
which condensation chemistry and the optical properties of grains is assuming
astronomical importance. In this short paper, I summarize the role played by
such refractories in determining the properties of these "stars" and the
complexities of their theoretical treatment.
