Abstract : The mechanisms of phase formation in thin films have been studied in the Al-Cu, Al-Fe, Fe-Cu and Al-Cu-Fe systems. Several samples with different compositions have been prepared by sputtering. Aluminium, copper and iron layers were deposited onto oxidized silicon substrates, they were heat treated and characterized by using several techniques. In situ X-ray diffraction and resistivity measurements were used to follow the phase formation. Thermal annealings followed by quenching have also been carried out to get additional information. Differential Scanning Calorimetry and coupled in-situ resistivity and X-ray diffraction measurements were performed. The whole results allowed us to suggest a mechanism of phase formation for each sample and by using theoretical models of growth we determined kinetic data on the phase formation.