We present evolutionary calculations for very-low-mass stars and brown dwarfs based on synthetic spectra and non-grey atmosphere models which include dust formation and opacity , i.e .
objects with T _ { eff } \hbox { \hbox { $ < $ } \kern - 8.0 pt \lower 4.3 pt \hbox { $ \sim$ } } 2800 K. The interior of the most massive brown dwarfs is shown to develop a conductive core after \sim 2 Gyr which slows down their cooling .
Comparison is made in optical and infrared color-magnitude diagrams with recent late-M and L-dwarf observations .
The saturation in optical colors and the very red near-infrared colors of these objects are well explained by the onset of dust formation in the atmosphere .
Comparison of the faintest presently observed L-dwarfs with these dusty evolutionary models suggests that dynamical processes such as turbulent diffusion and gravitational settling are taking place near the photosphere .
As the effective temperature decreases below T _ { eff } \approx 1300 - 1400 K , the colors of these objects move to very blue near-infrared colors , a consequence of the ongoing methane absorption in the infrared .
We suggest the possibility of a brown dwarf dearth in J,H,K color-magnitude diagrams around this temperature .

\keywords stars : low-mass , brown dwarfs — stars : evolution — stars : colour - magnitude diagrams