Résumé
I describe past and present models of AGB atmospheres, and their impact on abundances and parameter determinations. Without pretending to be exhaustive, I concentrate on recent achievements in that field. Despite the variable character of AGB star atmospheres, hydrostatic models are still useful in providing us with information, due to the great detail included now in their treatment of opacities. Hydrodynamic models in 1-D include detailed physics, like time-dependent dust formation, and the coupling between gas, dust and radiation, but are not able to treat the wavelength dependence of the radiation field in as much detail. Still, through their inclusion of dynamical phenomena they are a huge step forward. I show examples of comparisons of these models to observations, in particular spectroscopic, that should allow the establishment of powerful new diagnostic tools. I present also the efforts under way to produce 3-D radiative-hydrodynamic models. They should lead us to understanding the coupling between convection and pulsation in AGB stars, and the important asymmetries seen in their atmospheres.