  We present a spectroscopic classification system for M-dwarfs and M-subdwarfs
based on quantitative measures of TiO and CaH features in the region 6200 -
7400 Angstroms. Our sample of cool stars covers the range from solar
metallicity stars to the most extreme subdwarfs known. Using synthetic spectra
computed by Allard and Hauschildt (1995), we derive metallicities for the
stars. Stars are classified as dwarfs (M V), subdwarfs (sdM), or extreme
subdwarfs (esdM). These classifications correspond to [m/H] ~ 0.0, -1.2, and
-2.0 respectively. Our metallicity scale agrees with theoretical HR diagrams
and HST globular cluster measurements. We discuss some nearby subdwarfs of
particular interest in light of our metallicity scale.
