Good professional practice in the exploration of an engineering site is described in BS 5930:1981, Code of Practice for Site Investigations, which should be referred to by professional engineers as a source of definitions, and as an authoritative statement of the objects’ scope, procedures and methods of site investigation. It covers testing of mechanical and other properties of soils and rocks, which conventionally forms part of a civil engineering course taught by engineers. This chapter deals, however, only with the geological and geophysical surveys used to investigate what rocks and soils are present, and how they are distributed under the site.