Smithsonian Libraries (SIL), formerly known as Smithsonian Institution Libraries, is a library system comprising 20 branch libraries serving the various Smithsonian Institution museums and research centers, as well as central support services which include a Book Conservation Laboratory and an Imaging Center. The Libraries serve Smithsonian Institution staff as well as the scholarly community and general public with information and reference support. Its collections number over 1.5 million volumes including 40,000 rare books and 2,000 manuscripts. The Libraries also holds the United States' largest trade literature collection, which includes over 300,000 commercial catalogs dating from the early nineteenth century and representing more than 30,000 companies.