These libraries and archives hold the bulk of medieval manuscripts produced in or about medieval London.
London Metropolitan Archives (LMA) houses the largest collection of archival material on London and Londoners in the past. It was originally called the Greater London Record Office and History Library (GLRO), which itself was set up in 1965 with the merger of the London County Record Office, the London County Council Members Library, and the Middlesex County Record Office. In 2005, the LMA took over the former Corporation of London Record Office (CLRO), and re-cataloged its holdings. It is important to know about these changes since publications before 2005 list medieval documents now in the LMA with obsolete shelf-marks or numbers used in these earlier archives. There is a searchable online catalog and helpful downloadable Resource Guides. To identify medieval materials, start with the online Collections Catalog, but you are strongly advised to read the Help-Using the Catalogue page before starting any search. See also Digital Documents, which includes c. 150 digitized documents from before 1600, including the Letter Books.
The Guildhall Library holds over 200,000 printed books about London history, including many incunabula (materials printed before 1501). Its medieval archival collections include guild records and wills, but note that many medieval documents once in the Guildhall have now been moved to LMA. Its online catalog is now part of the LMA Collections Catalog.