ZnSe layers have been grown on (100)-oriented Ge substrates by molecular beam epitaxy for the first time. The optimum in-situ Ge substrate preparation technique was found to consist of argon-ion sputtering at room temperature followed by annealing at ∼400°C. This cleaning technique provided Ge surfaces which exhibited (2X2) surface reconstruction as observed by reflection high-energy electron diffraction and which had O and C contamination levels below the detection limit of the Auger electron spectroscopy system. ZnSe layers grown on argon-ion sputtered and annealed (100)Ge substrates using a variety of substrate temperatures and Zn to Se beam pressure ratios were characterized by 4.2 K photoluminescence (PL) measurements. The highest quality layers as judged by PL analysis were grown in the substrate temperature range, 310–350°C, with a Zn to Se beam pressure ratio around unity. ZnSe layers grown under these conditions exhibited a dominant donor-bound exciton peak at 2.7976 eV having a minimum linewidth of ∼1.1 meV.