Dust forming systems, in which a phase transition between the gas
phase and the solid state takes place, are seriously affected by the
presence of dust, which causes tight, non-linear interactions
between various physical and chemical processes. As a consequence,
the dynamics of, e.g., a stellar atmosphere and the formation of
dust grains are inseparably connected. Chemical conditions, dust
formation, and dust-induced instabilities in such non-linearly
coupled systems as well as some implications regarding stellar
evolution are discussed.