  We investigate the non-Local Thermodynamic Equilibrium (non-LTE) line
formation of neutral carbon in late-type stars in order to remove some of the
potential systematic errors in stellar abundance analyses employing C I
features. The statistical equilibrium code MULTI was used on a grid of
plane-parallel 1D MARCS atmospheric models. Within the parameter space
explored, the high-excitation C I lines are stronger in non-LTE due to the
combined effect of line source function drop and increased lower level
population; the relative importance of the two effects depends on the
particular combination of Teff, log g, [Fe/H] and [C/Fe] and on the analysed C
I line. As a consequence, the non-LTE abundance corrections are negative and
can be substantially so, for example ~-0.4 dex in halo turn-off stars at
[Fe/H]~-3. The magnitude of the non-LTE corrections is rather insensitive to
whether inelastic H collisions are included or not. Our results have
implications on studies of nucleosynthetic processes and on Galactic chemical
evolution models. When applying our calculated corrections to recent
observational data, the upturn in [C/O] at low metallicity might still be
present (thus apparently still necessitating contributions from massive Pop.
III stars for the carbon production), but at a lower level and possibly with a
rather shallow trend of ~-0.2 dex/dex below [O/H]~-1
