In this thesis the photoconductivity of polycrystallinerncadmium sulfide was investigated theoretically and experimentally.rnThe theory shows that both a change in carrier conent~rnration and mobility can contribute to the variation in conduc~"rntivity under illumination depending on the doping level, traprnconcentration and light intensity. Thin-film polycrystallinernlayers of CdS were prepared by the chemical bath depositionrntechnique. Doping with lithium was possible. X-ray investigationrnof the layers indicated that the layers are made up ofrnvery small crystallites. Annealing enhanced recrystallizationrnincreasing the crystallite dimension.rnBesides polycrystalline CdS, monocrystalline and pressedrnCdS were used for photoconductivity measurements. The annealedrnlayers showed a spectral photoresponse similar to the monocrystallinernCdS with an absorption edge at 2.4e'1. In order tornmeasure the lifetime of the charge carriers, the photoconductiverndecay process was used. The lifetime was found to have arnspectral dependence