Generally, the term document delivery means more specifically the supply of journal articles and other copies on a personalized basis, with the library charging the user or his academic department for the fees that are often involved.
Without interlibrary loans, if a library patron found an item they wanted, he would have to travel to that library, and apply for a local library card if eligible, or present a reciprocal card in order to borrow the item. By taking advantage of interlibrary loan, in comparison, the library staff can search large numbers of libraries at once, transport the item from several miles to thousands of miles away, and allow a patron to borrow the item using his or her local library card.
Interlibrary loan, or resource sharing, generally has two operations: borrowing and lending.
Commercial document delivery services can borrow on behalf of anyone willing to purchase the information.
Interlibrary loan and resource sharing have a variety of systems and workflow, often based on the scale of service, regional networks, and library systems. Processes are automated by computer systems such as VDX based on ISO ILL standards 10161 and 10160.
Loans requests between branch libraries in the same system may be filled in a brief amount of time, while loan requests between library systems may take weeks or more to be delivered. If an item is rare or difficult to find, this may be the easiest way to gain access to it. However, if an item is rare or difficult to find, interlibrary loan does not guarantee that the lending library will send the item through a local library. Some collections and volumes may be non-circulating. Urgent requests are placed if the item is needed urgently. These requests should be prioritized and supplied quickly. Books may be posted by courier and photocopies may be faxed or scanned and sent electronically. Additional fees may be charged for urgent service. Public libraries do not generally offer urgent service.
Traditionally, library users discovered potentially useful titles from book advertisements, through word-of-mouth from a friend or an authority on the subject, consulting the bibliographies found at the back of books or published as a separate book, or a printed union catalog of all the books in a group of libraries such as NUCMC. Requests were filled out on a standardized form and sent by postal mail to a library that allegedly owned a copy. This procedure is still used by libraries that are not members of an electronic interlibrary loan network. Since the mid-1980s, searching for books located at other libraries has become easier, as many libraries have allowed library users to search their online catalogs at the library or over the Internet.
Libraries have formed voluntary associations with each other to provide an online union catalog of all the items held by all member libraries. Whenever a library adds a new item to its catalog, a copy of the record is sent to update the union list. This allows libraries to quickly find out what other libraries hold an item, and software can facilitate the requesting and supplying of interlibrary loans. In the U.S., OCLC (Online Computer Library Center) is usually used by public and academic libraries, and RLIN (Research Libraries Information Network) is used primarily by academic libraries, although some libraries are members of both. Australia and New Zealand use Libraries Australia and Te Puna respectively, the national bibliographic networks of those countries.
Libraries that do not belong to a network can participate in interlibrary loan by making the arrangements by postal mail, fax, email or phone. Requests placed in one of these ways are referred to as manual requests.
Libraries may also have reciprocal arrangements with each other in order to supply loans and copies for free.
The leading journals in the field are: