A union catalog is a combined

library catalog A library catalog (or library catalogue in British English) is a register of all bibliographic items found in a library or group of libraries, such as a network of libraries at several locations. A catalog for a group of libraries is also c ...

describing the collections of a number of

libraries A library is a collection of materials, books or media that are accessible for use and not just for display purposes. A library provides physical (hard copies) or digital access (soft copies) materials, and may be a physical location or a vir ...

. Union catalogs have been created in a range of media, including

book A book is a medium for recording information in the form of writing or images, typically composed of many pages (made of papyrus, parchment, vellum, or paper) bound together and protected by a cover. The technical term for this physical arr ...

format,

microform Microforms are scaled-down reproductions of documents, typically either films or paper, made for the purposes of transmission, storage, reading, and printing. Microform images are commonly reduced to about 4% or of the original document size. F ...

card Card or The Card may refer to: * Various types of plastic cards: **By type ***Magnetic stripe card *** Chip card *** Digital card **By function ***Payment card ****Credit card **** Debit card ****EC-card ****Identity card ****European Health Insur ...

s and more recently, networked electronic

databases In computing, a database is an organized collection of data stored and accessed electronically. Small databases can be stored on a file system, while large databases are hosted on computer clusters or cloud storage. The design of databases spa ...

. Print union catalogs are typically arranged by title, author or subject (often employing a

controlled vocabulary Control may refer to: Basic meanings Economics and business * Control (management), an element of management * Control, an element of management accounting * Comptroller (or controller), a senior financial officer in an organization * Controlling ...

); electronic versions typically support keyword and Boolean queries. Union catalogs are useful to

librarian A librarian is a person who works professionally in a library providing access to information, and sometimes social or technical programming, or instruction on information literacy to users. The role of the librarian has changed much over time, ...

s, as they assist in locating and requesting materials from other libraries through

interlibrary loan Interlibrary loan (abbreviated ILL, and sometimes called interloan, interlending, document delivery, document supply, or interlibrary services, abbreviated ILS) is a service where patrons of one library can borrow materials and receive photocopies ...

service. They also allow researchers to search through collections to which they would not otherwise have access, such as

manuscript A manuscript (abbreviated MS for singular and MSS for plural) was, traditionally, any document written by hand – or, once practical typewriters became available, typewritten – as opposed to mechanically printing, printed or repr ...

collections. The largest union catalog ever printed is the American '' National Union Catalog Pre-1956 Imprints'' (NUC), completed in 1981. This achievement has since been superseded by the creation of union catalogs in the form of electronic databases, of which the largest is

OCLC OCLC, Inc., doing business as OCLC, See also: is an American nonprofit cooperative organization "that provides shared technology services, original research, and community programs for its membership and the library community at large". It was ...

WorldCat WorldCat is a union catalog that itemizes the collections of tens of thousands of institutions (mostly libraries), in many countries, that are current or past members of the OCLC global cooperative. It is operated by OCLC, Inc. Many of the OCL ...

. Another example is

COPAC Copac (originally an acronym of Consortium of Online Public Access Catalogues) was a union catalogue which provided free access to the merged online catalogues of many major research libraries and specialist libraries in the United Kingdom and Ire ...

provided by

Research Libraries UK Research Libraries UK (RLUK) (formerly CURL) comprises 32 university libraries, 3 national libraries, and the Wellcome Collection in the United Kingdom and Ireland. Its aim is to increase the ability of research libraries to share resources among ...

, which was superseded by Library Hub Discover in 2019. A third example is AMICUS, provided by

Library and Archives Canada Library and Archives Canada (LAC; french: Bibliothèque et Archives Canada) is the federal institution, tasked with acquiring, preserving, and providing accessibility to the documentary heritage of Canada. The national archive and library is th ...

. For academic publications, several

academic search engines This article contains a representative list of notable databases and search engines useful in an academic setting for finding and accessing articles in academic journals, institutional repositories, archives, or other collections of scientific and ...

exist to combine the

open data Open data is data that is openly accessible, exploitable, editable and shared by anyone for any purpose. Open data is licensed under an open license. The goals of the open data movement are similar to those of other "open(-source)" movements ...

provided by

open archive An open repository or open-access repository is a digital platform that holds research output and provides free, immediate and permanent access to research results for anyone to use, download and distribute. To facilitate open access such repositori ...

s through

OAI-PMH The Open Archives Initiative Protocol for Metadata Harvesting (OAI-PMH) is a protocol developed for harvesting metadata descriptions of records in an archive so that services can be built using metadata from many archives. An implementation of OAI-P ...

, as well as records from publishers deposited in CrossRef and other sources. They include BASE,

CORE Core or cores may refer to: Science and technology * Core (anatomy), everything except the appendages * Core (manufacturing), used in casting and molding * Core (optical fiber), the signal-carrying portion of an optical fiber * Core, the centra ...

and Unpaywall, which indexes over 20 million

open access Open access (OA) is a set of principles and a range of practices through which research outputs are distributed online, free of access charges or other barriers. With open access strictly defined (according to the 2001 definition), or libre op ...

publications as of 2020.

References

Library catalogues {{Library-stub