Detailed technical guidance is provided on the scope, planning, organisation, and appraisal of site investigations for civil engineering and building projects. The report relates generally to site investigation, although there is an emphasis throughout on geotechnical aspects, referred to as "ground investigation". The site investigation process is described, and guidance is given on the practical aspects of field work, laboratory testing of materials, interpretation of results and application to the design of foundations. Extensive coverage of sources of information, to assist the investigator during the preliminary studies, is presented as an appendix. Also appended is a comprehensive glossary of terms and definitions. Discussion is primarily based on investigation of soils and weak rocks occurring in Britain, stronger rocks being mentioned only superficially. Although many of the techniques and processes outlined are also applicable to ground investigation for roads, airfields, dams, tunnels, bridges and structures in general, the primary targets are for building foundations. There is also extensive application to overseas investigations. However, these have not been specifically considered. (Author/TRRL)