The British Architectural Library's manuscript and archives collection at the Royal Institute of British Architects (RIBA) is unrivalled in the breadth and extent of its holdings of unpublished materials relating to the theory and practice of architecture. The collection, which started soon after the founding of the RIBA in 1934, includes material dating from the early-17th century to the present day, ranging from an account of charges for the repair of Richmond Palace supervised by Inigo Jones in 1621-22, to the papers of Bernard Lubetkin. This work provides a practical guide to the contents and use of this large and important collection, and should enable researchers, librarians and archivists to locate original source material. The guide consists of 1500 entries arranged alphabetically, describing the groups of manuscripts in the collection with cross-references.