  We present evolutionary models for low mass stars from 0.075 to 1 $\msol$ for
solar-type metallicities [M/H]= 0 and -0.5. The calculations include the most
recent interior physics and the latest generation of non-grey atmosphere
models. We provide mass-age-color-magnitude relationships for both
metallicities. The mass-M$_V$ and mass-M$_K$ relations are in excellent
agreement with the empirical relations derived observationally. The theoretical
color-magnitude diagrams are compared with the sequences of globular clusters
(47 Tucanae) and open clusters (NGC2420 and NGC2477) observed with the Hubble
Space Telescope. Comparison is also made with field star sequences in
$M_V$-$(V-I)$, $M_K$-$(I-K)$ and $M_K$-$(J-K)$ diagrams. These comparisons show
that the most recent improvements performed in low-mass star atmosphere models
yield now reliable stellar models in the near-infrared. These models can be
used for metallicity, mass, temperature and luminosity calibrations.
Uncertainties still remain, however, in the optical spectral region below
$T_{eff} \sim 3700K$, where predicted (V-I) colors are too blue by 0.5 mag for
a given magnitude. The possible origins for such a discrepancy, most likely a
missing source of opacity in the optical and the onset of grain formation are
examined in detail.
