Halogen-terminated and organic functionalization of germanium (Ge) nanowires is described. X-ray photoelectron spectroscopy (XPS), X-ray photoemission electron microscopy (XPEEM), infrared spectroscopy (IR) and transmission electron microscopy were used to characterize the modified nanowire surfaces. The stability of alkyl and alkanethiol monolayers formed on Cl, Br and I-terminated surfaces are compared. The direct covalent attachment of aryl ligands onto H-Ge nanowires can be achieved by the decomposition of arenediazonium salts in acetonitrile solutions. The influenec of the ring substituent on the thickness and uniformity of the functionalization layer was investigated.