The sessile drop technique has been used to measure the wetting angle and the surface tension of molten germanium (Ge) on various substrate materials. Sapphire, fused silica, glassy carbon, graphite, SiC, carbon-based aerogel, pyrolytic boron nitride (pBN), AlN, Si3N4, and CVD diamond were used as substrate materials. In addition, the effects of different cleaning procedures and surface treatments on the wetting behavior were investigated. The highest wetting angles with values around 170 degrees were found for pBN substrates under active vacuum or with a slight overpressure of 5 N argon or forming g-as (2% hydrogen in 5N argon). The measurement of the surface tension and its temperature dependence for Ge under a forming gas atmosphere resulted in gamma (T) = 591 - 0.08 (T - T-m)[10(-3)N/m].