The crystallization of CuInSe2 thin films by high Se vapour selenization of co-sputtered Cu-In alloy precursor within a partially closed graphite container is reported. X-ray diffusion (XRD) analysis of the Cu-In alloy films displayed mainly the CuIn2 and Cu11In9 phases. A three-fold volume expansion was recorded in all the selenized CuInSe2 films at 500-550 degrees C. Large and densely packed crystals with sizes of about 5 mu m were exhibited by the films irrespective of whether they were Cu-rich or In-rich. Single phase chalcopyrite CuInSe2 structure with preferential orientation in the (112) direction were obtained. Films with a wide range of compositions (Cu/In of 0.43-1.2 and Se/(Cu + In) of 0.92-1.47) were fabricated. All the films where Se rich, with the exception of samples with very high Cu content. The measured film resistivities varied from 10(-1) to 10(5) Omega-cm in consistence with the increasing; Cu content of the alloy precursor during deposition. The alloy films with very high In content yielded the CuIn2Se3.5 or CuIn3Se5 compound as determined from XRD and EDX analyses. A study of the reaction mechanism performed between 250 and 550 degrees C indicated that the crystal growth was assisted by the formation of the CuSe flux agent. The development of a suitable window layer to test the photovoltaic properties of these films is currently in progress.