This study refers to an experimental research and contributes to a better understanding of corrosion and scaling in an operating geothermal power plant (Soultz-sous-Forêts, France). An in situ physicochemical monitoring program has been performed in order to characterise the processed brine. In situ and laboratory corrosion experiments were performed using conventional and candidate metals (mild steels, CrNiMo alloys, and non-ferrous metals). Mild steels exhibit long-term corrosion rates below 0.2 mm/year, accompanied by scaling formation offering protection. Conventional stainless steels 430F and 316L undergo pitting corrosion, while higher alloyed materials were identified to be suited for geothermal service.