Evolution of Low Mass Stars

We describe the evolution of low mass (1.5 < M=M < 0:02) stars and brown dwarfs starting from the hydrostatic phases of pre{main sequence contraction and evolving along the deuterium and lithium burning to reach the hydrogen burning main sequence or the brown dwarf degenerate cooling. With the help of new models computed by us, which we describe to the community taking advantage of this occasion, we focus our attention on some open problems of the models, which are relevant in the subsequent interpretation of observational data, namely: 1. The role of the convection treatment and opacities in determining the age, age distribution and mass function of young stellar populations; 2. The role of deuterium burning and of the protostellar phases of evolution in determining the \young" isochrones (t < 10 6 yr) location; 3. the great uncertainty in lithium depletion, and the inadequacy of our most recent models to describe the open cluster log N Li]{ T ee relations; the interesting fact that the boundary for lithium survival in brown dwarfs does not depend on detailed modeling; 4. the role of color { T ee relation in determining the location of the main sequence and the distance of open clusters