As the basis for structural design in particular, knowledge is required of the subsurface conditions – the soil and the groundwater. We compile expert reports according to the rules established by Eurocode 7 and DIN 4020. These consist of a site investigation program that is implemented through ground testing. The results are evaluated, the subsoil conditions are described, the relevant parameters are specified, and guidance is provided on the foundation, excavations, dewatering, earthworks, and the chemical behavior of the soil materials.