I will present the first results of a theoretical study aimed at 
analysing the near-to-mid infrared properties of giant stars, 
with particular attention focussed on the asymptotic giant branch 
(AGB) phase. On the base of calibrated synthetic TP-AGB stellar 
tracks, we perform population synthesis models to simulate 
photometry, surface chemistry, mass-loss rates, pulsation modes 
and periods of AGB stars. We take into account the effect of 
circumstellar dust during the mass-losing stages of the AGB 
evolution, so that simulations are also provided in the Spitzer 
and AKARI photometric systems.
I will discuss a few comparisons with observations of the Magellanic
Clouds and the globular cluster 47 Tuc.