  We present extensive calculations of the structure and the evolution of
low-massstars in the range 0.07-0.8 $\msol$, for metallicities $-2.0\le \mh \le
0.0$. These calculations are based on the most recent description of the
microphysics characteristic of these dense and cool objects and on the lattest
generation of grainless non-grey atmosphere models. We examine the evolution of
the different mechanical and thermal properties of these objects as a function
of mass and metallicity. We also demonstrate the inaccuracy of grey models and
$T(\tau)$ relationships under these conditions. We provide detailed tables of
the mass-radius-luminosity-effective temperature relations for various ages and
metallicities, aimed at calibrating existing or future observations of low-mass
stars and massive brown dwarfs. We derive new hydrogen-burning minimum masses,
within the afore-mentioned metallicity range. These minimum masses are found to
be smaller than previous estimates, a direct consequence of non-grey effects.
  At last, we examine the evolution of the abundance of light elements, $Li,
Be$ and $B$, as a function of age, mass and metallicity.
