Liquid metals are one of the most promising heat transfer fluids especially for higher temperatures. Lead alloy cooled fast reactors are one of the recent developments in nuclear energy while solar power plant (CSP) consider sodium as a heat transfer fluid and liquid tin is tested for direct methane conversion. One major drawback of all these energy related applications utilizing liquid metals are their high aggressiveness towards metallic structural materials. This presentation will cover the efforts at KIT on structural materials compatibility in liquid lead alloys including the development of aluminum containing alloys and surface treatments for steels which allow increasing the target operating temperature above 600°C. In sodium the main concern is the operation and thermal cycling of a system close to the liquids evaporation point temperature. Liquid tin is considered the most difficult material to master therefore ceramics like SiC, Maxthal and graphite are investigated.