The codeposition process of the Cu-In-Se system has been studied. Electrodeposited films were prepared and analyzed for their chemical composition before and after annealing treatment. The whole composition of the films depends on the diffusion flux ratios of the species arriving at the surface of the electrode. With an excess of In(III) in the solution, the ratio of the Se(IV) and the Cu(II) fluxes is the key parameter setting the composition. Lower concentrations of In(III) involve the deposition of elemental selenium. In this case, the electrodeposition process is limited by the diffusion of the three species. An estimation-of the diffusion fluxes is possible in order to predict the chemical composition of the films.