The kinetics of the phase transformations of the Fe-Si system and the Si/Fe and Fe/Si interfaces have been investigated by 57Fe conversion electron Mössbauer spectroscopy (CEMS). Single crystalline Fe films grown on Si(111) by molecular beam epitaxy (MBE) and polycrystalline Fe films grown by pulsed laser ablation deposition (PLD) have been thermally treated in vacuum and the formation of the different silicide phases has been monitored as function of temperature and time by CEMS.