Erfgoed Leiden en Omstreken (formerly Leiden Municipal Archives and Leiden Regional Archives) are in charge of some 6 kilometres of archives from local authorities and services, institutions and enterprises, monasteries, convents and churches, schools and factories, families en associations, notaries and courts of law. Alongside sources dealing with the city of Leiden and its inhabitants, there are also documents available on the neighbouring municipalities Leiderdorp, Rijnsburg, Warmond, Zoeterwoude and Noordwijk. Moreover, the Leiden Regional Archives have made three other collections available to visitors: the topographic historic atlas (more than 125,000 maps, photographs and prints), the historic library (more than 900 metres of books, periodicals, brochures and the like) and the poster collection (more than 5,000 posters).

Erfgoed Leiden en Omstreken is making good headway towards becoming a fully digitized archive. A Digital Genealogy database may already be consulted in the reading room; it includes baptism, marriage and burial registers from Leiden and entries originating from the municipal registries of Leiderdorp, Rijnsburg, Warmond en Zoeterwoude. But the Leiden Regional Archives have more in store, for instance a great project to digitize newspapers: the major newspapers that have appeared in Leiden through the years are being digitized in colour and made accessible through Optical Character Recognition.