First-hand study of built form is the essential basis for many studies of architecture as earlier chapters have shown, but there is a wide variety of other sources, both published and unpublished. If buildings do not survive in whole or part, then we have to rely solely on documentary evidence. Some projects may involve oral history and the use of the web. In this chapter we suggest major sources to look out for, indicate where they might be found and discuss their significance and uses. Where we begin and what we can discover depends on our aims and on the type of evidence available.