Asymptotic Giant Branch (AGB) stars are among the most important polluters of the interstellar medium. Their rich nucleosynthesis occurs in a wide range of temperatures and densities. Atoms are produced in their interiors, via charged particle reactions and thanks to the slow neutron capture process (the s-process). In their atmospheres, when the temperature drops below 5000 K, oxygen and carbon bearing molecules form, depending on the local C/O ratio. Further away from the central star, in their cool and expanded circumstellar envelopes, molecules cluster, leading to the formation of dust grains. I will present our stellar models (included in the FRUITY database), by describing how we model physical phenomena (as convection and rotation) as well as the ongoing nucleosynthesis. Moreover, I will introduce a new project aimed at modelling molecule and dust formation in the circumstellar envelopes of these objects, by highlighting pro and cons of our approach to the problem.