Building all, or some components, of buildings off site in a factory has been a feature of construction over many generations, and in some cases has been adopted extensively (eg door and window sets). Many terms have been used to describe this off-site construction (prefabrication, off-site assembly, factory assembly, pre-assembly, off-site manufacture, etc.). In this Guide the term 'off-site construction' will be used to refer to any part of the construction process that is carried out in controlled conditions away from the actual site where the building is or will be sited. In the post-war period, prefabricated construction unfortunately acquired negative connotations. However, with developments in lightweight, high strength materials and modern production techniques, prefabrication has much to offer today's construction industry. This Good Building Guide provides an introduction to the techniques and methods of off-site construction and suggests how these might be adopted within the modern construction process. Benefits include increased productivity and product quality. 8 pages.