opac

An Online Public Access Catalog (OPAC) is a searchable database of items held by a library, designed for public access. It allows users to locate physical materials such as books and media, as well as digital items, and to determine the item’s availability and location within the library system.

OPACs originated from traditional card catalogs and emerged with automated library systems in the late 20th century. Early interfaces were text-based, while modern OPACs are web-based and often form part of a broader discovery system that integrates catalog records with digital collections and other library services.

Core functions include searching by title, author, subject, ISBN, or keywords; browsing by subject headings or call numbers; and viewing item records that show metadata, availability status, library location, and shelf information. Users can place holds, renew items, and access digital resources linked from the catalog.

Technical underpinnings typically rely on MARC or other metadata formats, library management systems, and networking protocols. Historically Z39.50 provided cross-library search capability, while modern systems commonly use SRU/SRW or web APIs to enable retrieval and integration with discovery layers.

Access is usually available to the public through library networks, with authentication required for account features such as holds and renewals. OPACs continue to evolve with user-centric features, accessibility options, and integration with institutional repositories and digital collections, balancing search relevance with data quality and privacy concerns.