[en] This Guide discusses the geotechnical engineering aspects of the subsurface conditions and not the geological aspects except where these directly affect the foundation system. It discusses the geotechnical analyses required for the design of the nuclear power plant and indicates, in general, the site characteristics or geotechnical parameters that are required for these analyses. The parameters and site characteristics then form the subsurface design profile that allows geotechnical analyses to be performed in a consistent and compatible manner. There are many methods of field exploration, in situ testing and laboratory testing which allow the establishment of geotechnical parameters. These methods are discussed in this Guide together with their application to the siting and design phases. The type of information to be collected and investigation to be performed should be based on the analytical methods to be used in the proposed design. A brief indication of these methods is therefore included in this Guide