Eureka was the user interface

User interface

The user interface, in the industrial design field of human–machine interaction, is the space where interaction between humans and machines occurs. The goal of interaction between a human and a machine at the user interface is effective operation and control of the machine, and feedback from the...

 for general users of the Research Library Information Network (RLIN), a bibliographic resource containing records from libraries that were members of Research Libraries Group

Research Libraries Group

The Research Libraries Group was a U.S.-based library consortium which developed the Eureka interlibrary search engine, the RedLightGreen database of bibliographic descriptions and ArchiveGrid, a database containing descriptions of archival collections...

 (RLG). Eureka had the capacity to search among approximately 45 million different titles. Most of the catalog was from major research libraries and museums in the United States. Despite the OPAC

OPAC

An Online Public Access Catalog is an online database of materials held by a library or group of libraries...

 formulation, Eureka technically was not a public access search engine

Search engine

A search engine is an information retrieval system designed to help find information stored on a computer system. The search results are usually presented in a list and are commonly called hits. Search engines help to minimize the time required to find information and the amount of information...

. It was generally accessible only from networks connected to research institutions such as universities.

Following the 2006 merger of RLG into OCLC

OCLC

OCLC Online Computer Library Center, Inc. is "a nonprofit, membership, computer library service and research organization dedicated to the public purposes of furthering access to the world’s information and reducing information costs"...

, the Eureka databases were migrated to OCLC's FirstSearch in 2007.