The thermal evolution of reactively sputtered iron nitride thin films has been investigated by xray diffraction, Miissbauer conversion electron spectroscopy, transmission electron microscopy, and magnetic measurements. The results show that, independently of the original nitrogen content of the films, a similar composition of the end products after the 500 "C annealings is reached, being all composed of a-Fe plus "/-Fe, N in a wide range of relative proportions. The magnetic characteristics, however, are different depending on the nitrogen content of the as-deposited films.