Thin-film copper indium diselenide (CIS) was prepared by a process which involves two steps : (a) the formation of copper indium oxide by spray pyrolysis of an aqueous solution, and (b) subsequent reaction of the oxide with selenium vapour to form CIS. This technique provided oxide and selenide films with good purity and uniformity. During the oxide film formation two film growth mechanisms could be observed. The deposition efficiency of the spray pyrolysis step was rather high and dependent on the spray parameters, and a slight preference for Cu was observed. Conversion of the oxide film to the selenide caused an increase in film thickness and a further loss of indium. The resulting specular CIS films were soft and adhered well to the substrate. Conductivity and carrier type and density could be varied by control of the composition of the film.