The collection and services are used by people who choose not to — or cannot afford to — purchase an extensive collection themselves, who need material no individual can reasonably be expected to have, or who require professional assistance with their research.

However, with the collection of media other than books for storing information, many libraries are now also repositories and access points for maps, prints, or other documents and works of art on various storage media such as microform (microfilm/microfiche), audio tapes, CDs, LPs, cassettes, videotapes, and DVDs. Libraries may also provide public facilities to access CD-ROMs, subscription databases, and the Internet.

Thus, modern libraries are increasingly being redefined as places to get unrestricted access to information in many formats and from many sources. In addition to providing materials, they also provide the services of specialists, librarians, who are experts at finding and organizing information and at interpreting information needs.

More recently, libraries are understood as extending beyond the physical walls of a building, by including material accessible by electronic means, and by providing the assistance of librarians in navigating and analyzing tremendous amounts of knowledge with a variety of digital tools.

The term "library" has itself acquired a secondary meaning: "a collection of useful material for common use," and in this sense is used in fields such as computer science, mathematics and statistics, electronics and biology.

Antiquity

The first libraries were composed, for the most part, of unpublished records, a particular type of library called archives. Archaeological findings from the ancient city-states of Sumer have revealed temple rooms full of clay tablets in cuneiform script. These archives were made up almost completely of the records of commercial transactions or inventories, with only a few documents touching theological matters, historical records or legends. Things were much the same in the government and temple records on papyrus of Ancient Egypt.

The earliest discovered private archives were kept at Ugarit; besides correspondence and inventories, texts of myths may have been standardized practice-texts for teaching new scribes. There is also evidence of libraries at Nippur of about 1900 B.C. and those at Nineveh of about 700 B.C. as showing a library classification system.

Libraries in the Hellenic world and Rome