Interlibrary loan (abbreviated ILL, and sometimes called interloan, document delivery, or document supply) is a service whereby a user of one library can borrow books or receive photocopies of documents that are owned by another library. The user makes a request with their local library, which, acting as an intermediary, identifies owners of the desired item, places the request, receives the item, makes it available to the user, and arranges for its return. The lending library usually sets the due date and overdue fees of the material borrowed. Although books and journal articles are the most frequently requested items, some libraries will lend audio recordings, video recordings, maps, sheet music, and microforms of all kinds. In many cases, nominal fees accompany interlibrary loan services.
The term document delivery may also be used for a related service, namely the supply of journal articles and other copies on a personalized basis, whether these come from other libraries or direct from publishers. The end user is usually responsible for any fees, such as costs for postage or photocopying. Commercial document delivery services will borrow on behalf of any customer willing to pay their rates.
How interlibrary loan works 
Interlibrary loan, or resource sharing, has two operations: borrowing and lending.
- A borrowing library sends an owning library a request to borrow, photocopy, or scan materials needed by their patron.
- The owning library fills the request by sending materials to the borrowing library or supplies a reason why it cannot fill the request.
- If the item is sent, the borrowing library notifies the patron when the item arrives.
Interlibrary loan and resource sharing have a variety of systems and workflows, 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.
Loan requests between branch libraries in the same local library system are usually filled promptly, while loan requests between library systems may take weeks to complete. However, if an item is rare, fragile, or exceptionally valuable, the owning library is under no obligation to release it for interlibrary loan. Some collections and volumes, especially bound journals and one-of-a-kind manuscripts, are non-circulating, meaning that they may not be borrowed. Books may be delivered by mail or courier service. Photocopies may be faxed or scanned and delivered electronically. Urgent requests are placed if the item is needed right away, sometimes for additional fees. Public libraries do not usually offer urgent service.
United States 
In 1886 U.L. Rowell, Librarian at the University of California, Berkeley, sought permission to begin Interlibrary Loan; his request was granted during the years 1894-1898.
In 1894 Rowell initiated U.C. Berkeley's first program of interlibrary lending, with the California State Library as partner. Later that year Rowell expanded the invitation for a group of libraries, such as NUCMC. Librarians then filled out a standardized form (i.e. an ALA Interlibrary Loan Request Form 2002) and sent it by postal mail to a library that owned a copy. This procedure is still used by the few 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 enabled their users to search their online catalogs at the library or over the Internet. Today, everyone can freely use WorldCat.org to identify needed items that are not owned by his or her local libraries.
The Ohio State University and others in Ohio began integrating campus library systems at an early date. In the 1960s, state funds supported the development of the Online Computer Library Center (at that time called the Ohio College Library Center). OCLC has since grown into an international organization with a database of 30 million entries representing materials held in more than 10,000 libraries.
Resource sharing networks 
Libraries have established voluntary associations, often on a regional basis, to provide an online union catalog of all the items held by all member libraries. Whenever a library adds a new title to its catalog, a copy of the record is also added to the union list. This allows librarians to quickly determine which other libraries hold an item. Software then facilitates the request and supply tasks. In the U.S., Online Computer Library Center (OCLC) is used by public and academic libraries. Formerly, another network RLIN (Research Libraries Information Network) was used primarily by academic libraries but merged with OCLC on October 1, 2007. Australia and New Zealand use Libraries Australia and New Zealand Libraries' Catalogue respectively, the national bibliographic networks of those countries.
Online requests are usually submitted via OCLC's WorldCat or FirstSearch in the United States. Libraries without access to either can participate in interlibrary loan by submitting requests by postal mail, fax, email, or telephone. These are referred to as manual requests. Manual requests can be submitted in the United States by using an ALA (American Library Association) Interlibrary Loan Form.
Some libraries establish reciprocal arrangements with each other to supply loans and copies for free. Examples of such arrangements in the United States include Libraries Very Interested in Sharing (LVIS), Amigos, Mid-America Association of Law Libraries (MAALL), Bibliographical Center for Research, and the Greater Western Library Alliance (formerly the Big 12 Plus Library Consortium). Sometimes these arrangements include other services such as the Trans-Amigos Express (TAE) courier services which will ship and deliver items to Amigos members on the TAE route. Individual libraries can agree to reciprocal arrangements between each other.
Useful information for interlibrary loan users 
- Interlibrary loan policies and fees vary from country to country and library to library.
- New releases or high-demand titles are not always immediately available through ILL because most libraries need to satisfy local demand first. Similar limitations apply to textbooks.
- The patron requesting the item does not need to identify a library who owns it. Librarians offer this as a service for their patrons. For those who enjoy searching, however, the WorldCat website is the best place to look for items not owned by your local library. Many libraries have an online order form for interlibrary loan requests.
- If an item is not available from libraries in your own country, it is possible, although sometimes difficult, to get it from another country. Neighboring countries should be tapped first for faster turnaround time. Insurance and shipping charges may be an issue. Check with your local interlibrary loan staff regarding questions on these charges and whether any costs will be passed on to you.
- A rare book may be hard to obtain, but some libraries are willing to lend books that may be considered rare in other places. Rare items are almost always restricted to on-site use, meaning that the patron must use the book on library premises and will not be allowed to take it home. The alternatives are to look for a reprint or newer edition, search for the item at full-text or digitized book websites such as Project Gutenberg or Google Books, and if necessary, pay to have a microfilm copy made.
- Journals are not usually loaned; rather, a photocopy is made of the needed article. Some sources charge a copyright fee, which may be anywhere from $3 to $35 and sometimes higher. Policies vary about whether these fees are passed on to the patron.
- Aggarwal, Anil (2000). Web-Based Learning and Teaching Technologies: Opportunities and Challenges. Idea Group Inc. p. 21. ISBN 978-1-878289-60-5. OCLC 43095789.
- "Link+ Catalog". csul.iii.com. 2012 [last update]. Retrieved 4 March 2012.
- "What Is OhioLINK". ohiolink.edu. 2012 [last update]. Retrieved 4 March 2012. "OhioLINK"
- New Zealand Libraries' Catalogue — National Library of New Zealand
- http://www.ala.org/ala/mgrps/divs/rusa/archive/protools/referenceguide/illformprint.doc[dead link]
- http://www.cyberdriveillinois.com/departments/library/who_we_are/OCLC/programs_and_services/lvis_description.html[dead link]
- Amigos Library Services | Resource Sharing Through Technology
- Mid-America Association of Law Libraries
- http://www.amigos.org/?q=node/237[dead link]
Further reading 
- Boucher, Virginia. Interlibrary Loan Practices Handbook, 2nd Edition; American Library Association, Chicago and London, 1997
- Linda Frederiksen, Joel Cummings, Lara Cummings & Diane Carroll. (2011). Ebooks and Interlibrary Loan: Licensed to Fill? Journal of Interlibrary Loan,Document Delivery & Electronic Reserve. 21 (3), 117–131.
- Levine-Clark, Michael. (2011) Whither ILL? Wither ILL: The Changing Nature of Resource Sharing for E-Books. Collaborative Librarianship 3(2):71-72
- 2008 Document Delivery - Best Practices and Vendor Scorecard—Outsell, Inc.
- Journal of Library Administration; Volume 23, Numbers 1/2, 1996
The leading journals in the field of interlibrary loan are:
- Interlending and Document Supply
- Journal of Access Services
- Journal of Interlibrary Loan, Document Delivery and Electronic Reserve, Haworth Press. (Earlier title: Journal of Interlibrary Loan, Document Delivery & Information Supply).